drv update: version 0.94

git-svn-id: svn://tug.org/texlive/trunk@16096 c570f23f-e606-0410-a88d-b1316a301751

9 files changed, 945 insertions, 1067 deletions

diff --git a/Master/texmf-dist/doc/metapost/drv/README b/Master/texmf-dist/doc/metapost/drv/README
index e5d287c876f..31246497d23 100644
--- a/Master/texmf-dist/doc/metapost/drv/README
+++ b/Master/texmf-dist/doc/metapost/drv/README
@@ -1,5 +1,5 @@
 drv.mp - derivation trees with MetaPost
-version 0.93
+version 0.94
 
 Licence
 lppl
diff --git a/Master/texmf-dist/doc/metapost/drv/doc/drv-guide.mp b/Master/texmf-dist/doc/metapost/drv/doc/drv-guide.mp
index ab6b41675e2..8c5e207cafe 100644
--- a/Master/texmf-dist/doc/metapost/drv/doc/drv-guide.mp
+++ b/Master/texmf-dist/doc/metapost/drv/doc/drv-guide.mp
@@ -119,8 +119,10 @@ endfig;
 %
 
 beginfig(111)
-jgm 0 "A", "\vdash", "B";
+jgm 0 "A\vdash B";
+jgm 1 "A", "\vdash", "B";
 nfr 0 () ("f", 1);
+nfr 1 (0) ("f", 1);
 draw drv_tree;
 endfig;
 
@@ -271,10 +273,10 @@ draw drv_tree;
 endfig;
 
 vardef auxbox[]=
-  ((smin_x[@], ypart iln[ccl[@]].c+iln[ccl[@]].hg)--
-   (smin_x[@], smax_y[@])--
-   (smax_x[@], smax_y[@])--
-   (smax_x[@], ypart iln[ccl[@]].c+iln[ccl[@]].hg)--
+  ((sub_min_x[@], ypart iln[ccl[@]].c+iln[ccl[@]].hg)--
+   (sub_min_x[@], sub_max_y[@])--
+   (sub_max_x[@], sub_max_y[@])--
+   (sub_max_x[@], ypart iln[ccl[@]].c+iln[ccl[@]].hg)--
    cycle) shifted (0, min_clr_scl*min_clr[drv_sty]/2)
 enddef;
 
@@ -717,8 +719,6 @@ drv_scale (ilb, 1);
 % drv_junction_style
 %
 
-path azerty[];
-
 drv_junction_style 0;
 
 beginfig(300)
@@ -1507,8 +1507,8 @@ endfig;
 %
 
 drv_junction_style 0;
-drv_scale (jdg, 0.85);
-drv_scale (prm, 0.85);
+drv_scale (jdg, 0.9);
+drv_scale (prm, 0.9);
 
 vardef mix[]=
   "\textit{mix}("&(decimal @)&")"
@@ -1551,10 +1551,10 @@ nfr 0 (1) ("\text{contr$_g$, contr$_d$}", 1);
             nfr 8 () ("", 0);
         nfr 9 (mvd 10 (1, 6)) ("", 0);
           nfr 10 () ("", 0);
-      nfr 11 (12, 14) ("", 1);
+      nfr 11 (12, 14) (mix2, 1);
         nfr 12 (mvd 13 (1, 6)) ("", 0);
           nfr 13 () ("", 0);
-        nfr 14 (15) ("", 1);
+        nfr 14 (15) ("\vee_d", 1);
           nfr 15 (mvd 16 (1, 6)) ("", 0);
             nfr 16 () ("", 0);
     nfr 17 (18, 20) (mix4, 1);
diff --git a/Master/texmf-dist/doc/metapost/drv/doc/drv-guide.tex b/Master/texmf-dist/doc/metapost/drv/doc/drv-guide.tex
index 48a7644a517..02d0f8376c0 100644
--- a/Master/texmf-dist/doc/metapost/drv/doc/drv-guide.tex
+++ b/Master/texmf-dist/doc/metapost/drv/doc/drv-guide.tex
@@ -78,9 +78,9 @@ derivation trees with \MP%
 \thanks{Feel free to improve! (E.g. by correcting the poor English.)
 Last update: \today.}}}
 \author{Laurent \textsc{M\'ehats}\\
-{\small\href{mailto:laurent.mehats@gmail.com}
+{\small\href{mailto:laurent.mehats@gmail.com?subject=[drv 0.94]}
 {\texttt{laurent.mehats@gmail.com}}}}
-\date{documented version: 0.93}
+\date{documented version: 0.94}
 
 \pagestyle{myheadings}
 \renewcommand{\sectionmark}[1]{%
@@ -247,8 +247,10 @@ endfig;
 \begin{multicols}{2}
 \begin{Verbatim}
 beginfig(111)
-jgm 0 "A", "\vdash", "B";
+jgm 0 "A\vdash B";
+jgm 1 "A", "\vdash", "B";
 nfr 0 () ("f", 1);
+nfr 1 (0) ("f", 1);
 draw drv_tree;
 endfig;
 \end{Verbatim}
@@ -262,10 +264,10 @@ endfig;
 The outputs induced by
 \begin{center}
 \texttt{jgm 0 "A\tbs{}vdash B";}\qquad and\qquad
-\texttt{jgm 0 "A", "\tbs{}vdash", "B";}
+\texttt{jgm 1 "A", "\tbs{}vdash", "B";}
 \end{center}
 are the same. Using the latter declaration, you can manipulate sub-judgments
-independently from each-other (see \S~\ref{sec-components}).
+independently from each-other (see \S~\ref{sec-inside}).
 %
 %
 \paragraph{Inference line styles}
@@ -1214,7 +1216,7 @@ respect to a particular inference, judgment or sub-tree.\\[1ex]
 \begin{Verbatim}[commandchars=\\\{\}]
 beginfig(420)
 Dcl 0 ( ) ("",   "", "", _) "a";
-Dcl 1 (0) ("", "{}", "", _) "b";
+Dcl 1 (0) ("", "\{\}", "", _) "b";
 draw drv_tree;
 drv_axis (iln, 0);
 \resplap{}drv_axis (jdg, 1);
@@ -1837,6 +1839,10 @@ the \textsc{png} file you get is not transparent.
 {\texttt{bussproofs.sty}}
 (Samuel R. \textsc{Buss});
 \item
+\href{http://cristal.inria.fr/~remy/latex/}
+{\texttt{mathpartir.sty}}
+(Didier \textsc{R\'emy});
+\item
 \href{http://research.nii.ac.jp/~tatsuta/proof-sty.html}
 {\texttt{proof.sty}}
 (Makoto \textsc{Tatsuta});
@@ -1854,6 +1860,10 @@ metapost/contrib/macros/metaobj/}{\texttt{metaobj.mp}}
 {\texttt{semantic.sty}}
 (Peter M\o ller \textsc{Neergaard} \& Arne John \textsc{Glenstrup});
 \item
+\href{http://www.utdallas.edu/~hamlen/projects.html}
+{\texttt{trfrac.sty}}
+(Kevin W. \textsc{Hamlen});
+\item
 \href{http://alessio.guglielmi.name/res/vl/}
 {\texttt{virginialake.sty}}
 (Alessio \textsc{Guglielmi}).
diff --git a/Master/texmf-dist/doc/metapost/drv/doc/drv.mp b/Master/texmf-dist/doc/metapost/drv/doc/drv.mp
index 5eb38396144..69f2f9f72c7 100644
--- a/Master/texmf-dist/doc/metapost/drv/doc/drv.mp
+++ b/Master/texmf-dist/doc/metapost/drv/doc/drv.mp
@@ -1,4 +1,4 @@
-%% drv.mp 0.93
+%% drv.mp 0.94
 %% Copyright 2009 Laurent M\'ehats
 %
 % This work may be distributed and/or modified under the
@@ -188,10 +188,10 @@
 %
 %   drv_left_delimiter <str>
 %	<str>		left delimiter math-mode LaTeX code
-%			  "("	$($
-%			  "["	$[$
-%			  "\lbrace"	$\lbrace$
-%			  "\langle"	$\langle$
+%			  "("
+%			  "["
+%			  "\lbrace"
+%			  "\langle"
 %			  etc.
 %
 %   drv_right_delimiter <str>
@@ -391,8 +391,8 @@ drv_message "done.";
 % writing LaTeX picture definitions
 %
 
-numeric tex_pct_idx;
-tex_pct_idx:=0;
+numeric tex_pct_rnk;
+tex_pct_rnk:=0;
 
 % Math style indices: 0, 1, 2, 3
 string mth_sty_str[];
@@ -410,14 +410,14 @@ vardef drv_tex[] expr tex_str=
   string def_str;
   picture pct;
   def_str:="btex{"&drv_fontsize&"$"&mth_sty_str[@]&"{}"&tex_str&"{}$}etex;";
-  write "tex_pct["&(decimal tex_pct_idx)&"]:="&def_str to delayed_tex_file;
+  write "tex_pct["&(decimal tex_pct_rnk)&"]:="&def_str to delayed_tex_file;
   pct:=
-    if known tex_pct[tex_pct_idx]:
-      tex_pct[tex_pct_idx]
+    if known tex_pct[tex_pct_rnk]:
+      tex_pct[tex_pct_rnk]
     else:
       nullpicture
     fi;
-  tex_pct_idx:=tex_pct_idx+1;
+  tex_pct_rnk:=tex_pct_rnk+1;
   pct
 enddef;
 
@@ -644,31 +644,31 @@ vardef drv_beginfig=
   numeric iln_sty[];
   numeric l_prm[], r_prm[];
   %
-  % imin_x[i]	inference minimal x
-  % l_dlb[i]	left delimiter label drv-box
-  % l_dlm[i]	left delimiter drv-box
-  % l_ilb[i]	left label drv-box
-  % iln[i]	inference line drv-box
-  % r_ilb[i]	right label drv-box
-  % r_dlm[i]	right delimiter drv-box
-  % r_dlb[i]	right delimiter label drv-box
-  % imax_x[i]	inference maximal x
+  % nfr_min_x[i]	inference minimal x
+  % l_dlb[i]		left delimiter label drv-box
+  % l_dlm[i]		left delimiter drv-box
+  % l_ilb[i]		left label drv-box
+  % iln[i]		inference line drv-box
+  % r_ilb[i]		right label drv-box
+  % r_dlm[i]		right delimiter drv-box
+  % r_dlb[i]		right delimiter label drv-box
+  % nfr_max_x[i]	inference maximal x
   %
-  numeric imin_x[];
+  numeric nfr_min_x[];
   drv_box "l_dlb[]", "l_dlm[]", "l_ilb[]";
   drv_box "iln[]";
   drv_box "r_ilb[]", "r_dlm[]", "r_dlb[]";
-  numeric imax_x[];
+  numeric nfr_max_x[];
   %
   % Sub-trees
   %
-  % smin_x[i]	sub-tree minimal x
-  % smax_x[i]	sub-tree maximal x
-  % smin_y[i]	sub-tree minimal y
-  % smax_y[i]	sub-tree maximal y
-  % boxed[i]	boolean
+  % sub_min_x[i]	sub-tree minimal x
+  % sub_max_x[i]	sub-tree maximal x
+  % sub_min_y[i]	sub-tree minimal y
+  % sub_max_y[i]	sub-tree maximal y
+  % boxed[i]		boolean
   %
-  numeric smin_x[], smax_x[], smin_y[], smax_y[];
+  numeric sub_min_x[], sub_max_x[], sub_min_y[], sub_max_y[];
   boolean boxed[];
   %
   % Pen initialization
@@ -694,14 +694,13 @@ vardef drv_beginfig=
   %
   % root_num	number of roots
   % root[i]	root index (i ranges from 0 to root_num-1)
-  % drv_built	boolean
+  % drv_checked	boolean
   % drv_frozen	boolean
   %
   numeric root_num, root[];
-  boolean drv_checked, drv_built, drv_frozen;
+  boolean drv_checked, drv_frozen;
   root_num:=0;
   drv_checked:=false;
-  drv_built:=false;
   drv_frozen:=false;
   %
   % Phantom steps
@@ -819,27 +818,19 @@ vardef jgm[] text SUB=
     jdg_wd:=0;
     sbj_rnk:=0;
     for sub=SUB:
-      sbj_pct:=
-        if picture sub:
-          sub
-        elseif sub<>"":
-          mth_tex[jdg_sty[drv_sty]] sub
-        else:
-          nullpicture
-        fi;
+      sbj_pct:=mth_tex[jdg_sty[drv_sty]] sub;
       box_init sbj[@][sbj_rnk] (sbj_pct);
-      if sbj_rnk>0:
-        sbj[@][sbj_rnk-1].r=sbj[@][sbj_rnk].l;
+      if sbj_rnk>0:				% non mandatory test
+        sbj[@][sbj_rnk-1].r=sbj[@][sbj_rnk].l;	% irrelevant if rnk=0
       fi
       addto jdg_pct also sbj_pct shifted (jdg_wd, 0);
-      jdg_wd:=width jdg_pct;
+      jdg_wd:=jdg_wd+width sbj_pct;
       sbj_rnk:=sbj_rnk+1;
     endfor
     sbj_num[@]:=sbj_rnk;
     box_init jdg[@] (jdg_pct);
-    if sbj_num[@]>0:
-      jdg[@].l=sbj[@][0].l;
-      jdg[@].r=sbj[@][sbj_num[@]-1].r;
+    if sbj_num[@]>0:				% non mandatory test
+      jdg[@].l=sbj[@][0].l;			% irrelevant if sbj_num=0
     fi
   fi
 enddef;
@@ -850,6 +841,19 @@ enddef;
 % Inference declarations
 %
 
+%
+% 1. Global parameters
+%
+
+numeric drv_jct_sty;	% default junction style
+string  drv_alg_sty;	% default junction style
+numeric drv_iln_sty;	% default inference line path-style
+numeric drv_phm_sty;	% default phantom steps path-style
+
+%
+% 2. Macros
+%
+
 vardef check_junction_style (suffix sty_sfx) (expr default)=
   save sty_str;
   string sty_str;
@@ -931,13 +935,9 @@ vardef check_path_style (suffix sty_sfx) (expr default)=
   fi
 enddef;
 
-vardef opt_init[] @# expr arg=
-  if picture arg:
-    if arg<>nullpicture:
-      box_init @# (arg);
-    fi
-  elseif arg<>"":
-    box_init @# (mth_tex[@] arg);
+vardef opt_init[] @# expr str=
+  if str<>"":
+    box_init @# (mth_tex[@] str);
   fi
 enddef;
 
@@ -971,17 +971,17 @@ vardef NFR[] (text PRM) (expr lilb, rilb, ldlb, rdlb)
           %
           % roots list update
           %
-          save root_idx;
-          numeric root_idx;
-          root_idx:=0;
+          save root_rnk;
+          numeric root_rnk;
+          root_rnk:=0;
           forever:
-            exitif root[root_idx]=prm_idx;
-            root_idx:=root_idx+1;
+            exitif root[root_rnk]=prm_idx;
+            root_rnk:=root_rnk+1;
           endfor
           forever:
-            exitif root_idx=root_num-1;
-            root[root_idx]:=root[root_idx+1];
-            root_idx:=root_idx+1;
+            exitif root_rnk=root_num-1;
+            root[root_rnk]:=root[root_rnk+1];
+            root_rnk:=root_rnk+1;
           endfor
           root_num:=root_num-1;
         fi
@@ -1033,9 +1033,6 @@ vardef NFR[] (text PRM) (expr lilb, rilb, ldlb, rdlb)
     jct_sty[@]:=check_junction_style (j_sty, drv_jct_sty);
     alg_sty[@]:=check_alignment_style (a_sty, drv_alg_sty);
     iln_sty[@]:=check_path_style (i_sty, drv_iln_sty);
-    if drv_boxmode_on:
-      boxed[@]:=true;
-    fi
   fi
 enddef;
 
@@ -1051,23 +1048,23 @@ vardef MVD[] (expr inf_num, lplb, rplb) (suffix a_sty, p_sty)=
     drv_errmessage (decimal inf_num)&" is not a valid number of inference"&
       " steps";
   else:
-    save aux_idx, aux_sty, phm_jdg;
-    numeric aux_idx, aux_sty;
+    save prm_idx, pth_sty, phm_jdg;
+    numeric prm_idx, pth_sty;
     picture phm_jdg;
-    aux_sty:=check_path_style (p_sty, drv_phm_sty);
+    pth_sty:=check_path_style (p_sty, drv_phm_sty);
     phm_jdg:=nullpicture;
-    setbounds phm_jdg to (0, 0)--(iln_hg[aux_sty]-iln_dp[aux_sty], 0)--cycle;
-    aux_idx:=@;
+    setbounds phm_jdg to (0, 0)--(iln_hg[pth_sty]-iln_dp[pth_sty], 0)--cycle;
+    prm_idx:=@;
     for i=1 upto inf_num:
       phm_idx:=phm_idx-1;
       box_init jdg[phm_idx] (phm_jdg);
       sbj_num[phm_idx]:=0;
-      NFR[phm_idx] (aux_idx) ("", "", "", "", 0, a_sty, 0);
-      aux_idx:=phm_idx;
+      NFR[phm_idx] (prm_idx) ("", "", "", "", 0, a_sty, 0);
+      prm_idx:=phm_idx;
     endfor
     src[@]:=phm_idx;
     tgt[phm_idx]:=@;
-    phm_sty[phm_idx]:=aux_sty;
+    phm_sty[phm_idx]:=pth_sty;
     %
     % lplb, rplb: phantom steps labels
     %
@@ -1086,33 +1083,20 @@ enddef;
 % Optional labels & shorthands
 %
 
-numeric drv_jct_sty;	% default junction style
-string  drv_alg_sty;	% default junction style
-numeric drv_iln_sty;	% default inference line path-style
-numeric drv_phm_sty;	% default phantom steps path-style
-
 boolean drv_left_ilb;	% inference labels on the left
 boolean drv_left_dlb;	% delimiter labels (hence delimiters) on the left
 boolean drv_left_plb;	% phantom steps labels on the left
 
-vardef arg_type expr arg=
-  if picture arg:
-    "picture"
-  else:
-    "string"
-  fi
-enddef;
-
 vardef opt_lbls @# (text LBL) expr left_lbls=
   save lbl_num, fst_lbl, snd_lbl;
   numeric lbl_num;
   lbl_num:=0;
   for lbl=LBL:
     if lbl_num=0:
-      scantokens (arg_type lbl) fst_lbl;
+      string fst_lbl;
       fst_lbl:=lbl;
     elseif lbl_num=1:
-      scantokens (arg_type lbl) snd_lbl;
+      string snd_lbl;
       snd_lbl:=lbl;
     else:
       drv_errhelp "At most two labels can be specified:"&
@@ -1121,26 +1105,20 @@ vardef opt_lbls @# (text LBL) expr left_lbls=
     fi
     lbl_num:=lbl_num+1;
   endfor
+  string @#.l;
+  string @#.r;
   if lbl_num=0:
-    string @#.l;
-    string @#.r;
     @#.l:="";
     @#.r:="";
   elseif lbl_num=1:
     if left_lbls:
-      scantokens (arg_type fst_lbl) @#.l;
-      string @#.r;
       @#.l:=fst_lbl;
       @#.r:="";
     else:
-      string @#.l;
-      scantokens (arg_type fst_lbl) @#.r;
       @#.l:="";
       @#.r:=fst_lbl;
     fi
   else:
-    scantokens (arg_type fst_lbl) @#.l;
-    scantokens (arg_type snd_lbl) @#.r;
     @#.l:=fst_lbl;
     @#.r:=snd_lbl;
   fi
@@ -1339,8 +1317,8 @@ enddef;
 % 1. Global parameters
 %
 
-string drv_l_dlm; % left delimiter LaTeX code
-string drv_r_dlm; % right delimiter LaTeX code
+string drv_ldlm_str; % left delimiter LaTeX code
+string drv_rdlm_str; % right delimiter LaTeX code
 
 %
 % 2. Macros
@@ -1352,16 +1330,16 @@ vardef minmax_y[]=(
       ypart jdg[@].c-num_hg+iln_hg[(iln_sty[ccl[@]])]
         +min_clr_scl*min_clr[drv_sty]/2
     else:
-      smin_y[@]-min_clr_scl*min_clr[drv_sty]
+      sub_min_y[@]-min_clr_scl*min_clr[drv_sty]
     fi,
-    smax_y[@]+min_clr_scl*min_clr[drv_sty]
+    sub_max_y[@]+min_clr_scl*min_clr[drv_sty]
   else:
-    smin_y[@]-min_clr_scl*min_clr[drv_sty],
+    sub_min_y[@]-min_clr_scl*min_clr[drv_sty],
     if known ccl[@]:
-      ypart jdg[@].c-den_dp-iln_hg[(iln_sty[ccl[@]])]
+      ypart jdg[@].c-den_dp+iln_dp[(iln_sty[ccl[@]])]
         -min_clr_scl*min_clr[drv_sty]/2
     else:
-      smax_y[@]+min_clr_scl*min_clr[drv_sty]
+      sub_max_y[@]+min_clr_scl*min_clr[drv_sty]
     fi
   fi)
 enddef;
@@ -1374,9 +1352,9 @@ vardef delim @# expr dlm_len=
   rule_str:="\rule{0bp}{"&(decimal(dlm_len/2+axis_hg[drv_sty]))&"bp}";
   dlm_str:=
     if str @#="l":
-      "\left"&drv_l_dlm&rule_str&"\right."
+      "\left"&drv_ldlm_str&rule_str&"\right."
     else:
-      "\left."&rule_str&"\right"&drv_r_dlm
+      "\left."&rule_str&"\right"&drv_rdlm_str
     fi;
   dlm_pct:=mth_tex[drv_sty] dlm_str;
   dlm_dp:=depth dlm_pct;
@@ -1472,7 +1450,7 @@ vardef drv_check_root[]=
       fi
     fi
     if unknown boxed[@]:
-      boxed[@]:=false;
+      boxed[@]:=drv_boxmode_on;
     fi
   fi
 enddef;
@@ -1490,8 +1468,8 @@ vardef drv_check=
       save root_str;
       string root_str;
       root_str:=decimal root_idx;
-      for idx=1 upto root_num-1:
-        root_idx:=root[idx];
+      for root_rnk=1 upto root_num-1:
+        root_idx:=root[root_rnk];
         drv_check_root[root_idx];
         root_str:=root_str&", "&(decimal root_idx);
       endfor
@@ -1507,70 +1485,96 @@ enddef;
 
 vardef drv_build_root[]=
   %
+  % orientation
+  %
+  if drv_bot_roots:
+    ypart iln[@].c=ypart jdg[@].c-den_dp;
+    sub_min_y[@]:=ypart jdg[@].c+jdg[@].dp;
+    sub_max_y[@]:=
+      if iln_sty[@]=0:
+        ypart jdg[@].c+jdg[@].hg
+      else:
+        ypart iln[@].c+iln_hg[iln_sty[@]]
+      fi;
+    for prm_rnk=0 upto prm_num[@]-1:
+      ypart jdg[prm[@][prm_rnk]].c=ypart iln[@].c+num_hg;
+      drv_build_root[prm[@][prm_rnk]];
+      sub_max_y[@]:=max(sub_max_y[@], sub_max_y[prm[@][prm_rnk]]);
+    endfor
+  else:
+    ypart iln[@].c=ypart jdg[@].c-num_hg;
+    sub_min_y[@]:=
+      if iln_sty[@]=0:
+        ypart jdg[@].c+jdg[@].dp
+      else:
+        ypart iln[@].c+iln_dp[iln_sty[@]]
+      fi;
+    sub_max_y[@]:=ypart jdg[@].c+jdg[@].hg;
+    for prm_rnk=0 upto prm_num[@]-1:
+      ypart jdg[prm[@][prm_rnk]].c=ypart iln[@].c+den_dp;
+      drv_build_root[prm[@][prm_rnk]];
+      sub_min_y[@]:=min(sub_min_y[@], sub_min_y[prm[@][prm_rnk]]);
+    endfor
+  fi
+  %
   % premises junction (from left to right)
   %
-  for prm_rnk=0 upto  prm_num[@]-1:
-    drv_build_root[prm[@][prm_rnk]];
-    if prm_rnk>0:
-      save ll_idx, lr_idx, rl_idx, rr_idx;
-      save lmax_x, rmin_x, min_skp;
-      numeric ll_idx, lr_idx, rl_idx, rr_idx;
-      numeric lmax_x, rmin_x, min_skp;
-      ypart jdg[prm[@][prm_rnk-1]].c=ypart jdg[prm[@][prm_rnk]].c;
-      ll_idx:=prm[@][0];
-      lr_idx:=prm[@][prm_rnk-1];
-      rl_idx:=prm[@][prm_rnk];
-      rr_idx:=prm[@][prm_rnk];
-      lmax_x:=imax_x[lr_idx];
-      rmin_x:=imin_x[rl_idx];
-      min_skp[0]:=rmin_x-lmax_x;
-      forever:
-        exitif (unknown r_prm[lr_idx]) or (unknown l_prm[rl_idx]);
-        ll_idx:=l_prm[ll_idx];
-        lr_idx:=r_prm[lr_idx];
-        rl_idx:=l_prm[rl_idx];
-        rr_idx:=r_prm[rr_idx];
-        lmax_x:=max(lmax_x, imax_x[lr_idx]);
-        rmin_x:=min(rmin_x, imin_x[rl_idx]);
-        min_skp[0]:=min(min_skp[0], imin_x[rl_idx]-imax_x[lr_idx]);
-      endfor
-      min_skp[1]:=rmin_x-lmax_x;
-      if known r_prm[lr_idx]:
-        r_prm[rr_idx]:= r_prm[lr_idx];
-        lmax_x:=smax_x[lr_idx];
-      elseif known l_prm[rl_idx]:
-        l_prm[ll_idx]:=l_prm[rl_idx];
-        rmin_x:=smin_x[rl_idx];
-      fi
-      min_skp[2]:=rmin_x-lmax_x;
-      if jct_sty[@]<3:
-        min_skp[jct_sty[@]]=prm_skp_scl*prm_skp[drv_sty];
-      fi
+  for prm_rnk=1 upto  prm_num[@]-1:
+    save l_lmost, l_rmost, r_lmost, r_rmost;
+    save l_max_x, r_min_x, min_skp;
+    numeric l_lmost, l_rmost, r_lmost, r_rmost;
+    numeric l_max_x, r_min_x, min_skp[];
+    l_lmost:=prm[@][0];
+    l_rmost:=prm[@][prm_rnk-1];
+    r_lmost:=prm[@][prm_rnk];
+    r_rmost:=prm[@][prm_rnk];
+    l_max_x:=nfr_max_x[l_rmost];
+    r_min_x:=nfr_min_x[r_lmost];
+    min_skp[0]:=r_min_x-l_max_x;
+    forever:
+      exitif (unknown r_prm[l_rmost]) or (unknown l_prm[r_lmost]);
+      l_lmost:=l_prm[l_lmost];
+      l_rmost:=r_prm[l_rmost];
+      r_lmost:=l_prm[r_lmost];
+      r_rmost:=r_prm[r_rmost];
+      l_max_x:=max(l_max_x, nfr_max_x[l_rmost]);
+      r_min_x:=min(r_min_x, nfr_min_x[r_lmost]);
+      min_skp[0]:=min(min_skp[0], nfr_min_x[r_lmost]-nfr_max_x[l_rmost]);
+    endfor
+    min_skp[1]:=r_min_x-l_max_x;
+    if known r_prm[l_rmost]:
+      r_prm[r_rmost]:= r_prm[l_rmost];
+      l_max_x:=sub_max_x[l_rmost];
+    elseif known l_prm[r_lmost]:
+      l_prm[l_lmost]:=l_prm[r_lmost];
+      r_min_x:=sub_min_x[r_lmost];
+    fi
+    min_skp[2]:=r_min_x-l_max_x;
+    if jct_sty[@]<3:
+      min_skp[jct_sty[@]]=prm_skp_scl*prm_skp[drv_sty];
     fi
   endfor
-  if  prm_num[@]>0:
-    l_prm[@]:=prm[@][0];
-    r_prm[@]:=prm[@][prm_num[@]-1];
-  fi
   %
   % judgment alignment
   %
   if prm_num[@]=0:
-    imin_x[@]:=xpart jdg[@].l-jdg_skp_scl*jdg_skp[jdg_sty[drv_sty]];
-    imax_x[@]:=xpart jdg[@].r+jdg_skp_scl*jdg_skp[jdg_sty[drv_sty]];
+    nfr_min_x[@]:=xpart jdg[@].l;
+    nfr_max_x[@]:=xpart jdg[@].r;
   else:
+    l_prm[@]:=prm[@][0];
+    r_prm[@]:=prm[@][prm_num[@]-1];
     save l_xref, r_xref;
     l_xref=
-      if boxed[prm[@][0]]:
-        smin_x[prm[@][0]]
+      if boxed[l_prm[@]]:
+        sub_min_x[l_prm[@]]
       else:
-        xpart jdg[prm[@][0]].l
+        xpart jdg[l_prm[@]].l
       fi;
     r_xref=
-      if boxed[prm[@][prm_num[@]-1]]:
-        smax_x[prm[@][prm_num[@]-1]]
+      if boxed[r_prm[@]]:
+        sub_max_x[r_prm[@]]
       else:
-        xpart jdg[prm[@][prm_num[@]-1]].r
+        xpart jdg[r_prm[@]].r
       fi;
     if alg_sty[@]="l":
       xpart jdg[@].l=l_xref;
@@ -1579,10 +1583,8 @@ vardef drv_build_root[]=
     elseif alg_sty[@]="r":
       xpart jdg[@].r=r_xref;
     fi
-    imin_x[@]:=min(xpart jdg[@].l, l_xref)
-          -jdg_skp_scl*jdg_skp[jdg_sty[drv_sty]];
-    imax_x[@]:=max(xpart jdg[@].r, r_xref)
-          +jdg_skp_scl*jdg_skp[jdg_sty[drv_sty]];
+    nfr_min_x[@]:=min(xpart jdg[@].l, l_xref);
+    nfr_max_x[@]:=max(xpart jdg[@].r, r_xref);
   fi
   %
   % inference line
@@ -1590,7 +1592,7 @@ vardef drv_build_root[]=
   save iln_wd, iln_pct;
   numeric iln_wd;
   picture iln_pct;
-  iln_wd:=imax_x[@]-imin_x[@];
+  iln_wd:=nfr_max_x[@]-nfr_min_x[@]+2*jdg_skp_scl*jdg_skp[jdg_sty[drv_sty]];
   iln_pct:=((0, 0)--(iln_wd, 0)) drv_styled iln_sty[@];
   setbounds iln_pct to
     (0, ypart llcorner iln_pct)
@@ -1599,65 +1601,33 @@ vardef drv_build_root[]=
   --(iln_wd, ypart llcorner iln_pct)
   --cycle; % ! `linecap:=butt' and `linecap:=squared' -> same bounding box !
   box_init iln[@] (iln_pct);
-  xpart iln[@].c=(imin_x[@]+imax_x[@])/2;
-  %
-  % orientation, smin_y & smax_y
-  %
-  if drv_bot_roots:
-    ypart iln[@].c=ypart jdg[@].c-den_dp;
-    smin_y[@]:=ypart jdg[@].c+jdg[@].dp;
-    smax_y[@]:=
-      if iln_sty[@]=0:
-        ypart jdg[@].c+jdg[@].hg
-      else:
-        ypart iln[@].c+iln[@].hg
-      fi;
-    if prm_num[@]>0:
-      ypart iln[@].c=ypart jdg[prm[@][0]].c-num_hg;
-      for prm_rnk=0 upto prm_num[@]-1:
-        smax_y[@]:=max(smax_y[@], smax_y[prm[@][prm_rnk]]);
-      endfor;
-    fi
-  else:
-    ypart iln[@].c=ypart jdg[@].c-num_hg;
-    smin_y[@]:=
-      if iln_sty[@]=0:
-        ypart jdg[@].c+jdg[@].dp
-      else:
-        ypart iln[@].c+iln[@].dp
-      fi;
-    smax_y[@]:=ypart jdg[@].c+jdg[@].hg;
-    if prm_num[@]>0:
-      ypart iln[@].c=ypart jdg[prm[@][0]].c-den_dp;
-      for prm_rnk=0 upto prm_num[@]-1:
-        smin_y[@]:=min(smin_y[@], smin_y[prm[@][prm_rnk]]);
-      endfor;
-    fi
+  xpart iln[@].c=(nfr_min_x[@]+nfr_max_x[@])/2;
+  if iln_sty[@]>0:
+    nfr_min_x[@]:=xpart iln[@].l;
+    nfr_max_x[@]:=xpart iln[@].r;
   fi
   %
   % inference labels
   %
   if known l_ilb[@]:
     l_ilb[@].r=iln[@].l shifted (-ilb_skp_scl*ilb_skp[drv_sty], 0);
-    imin_x[@]:=xpart l_ilb[@].l;
-    smin_y[@]:=min(smin_y[@], ypart l_ilb[@].c+l_ilb[@].dp);
-    smax_y[@]:=max(smax_y[@], ypart l_ilb[@].c+l_ilb[@].hg);
+    nfr_min_x[@]:=xpart l_ilb[@].l;
+    sub_min_y[@]:=min(sub_min_y[@], ypart l_ilb[@].c+l_ilb[@].dp);
+    sub_max_y[@]:=max(sub_max_y[@], ypart l_ilb[@].c+l_ilb[@].hg);
   fi
   if known r_ilb[@]:
     r_ilb[@].l=iln[@].r shifted (ilb_skp_scl*ilb_skp[drv_sty], 0);
-    imax_x[@]:=xpart r_ilb[@].r;
-    smin_y[@]:=min(smin_y[@], ypart r_ilb[@].c+r_ilb[@].dp);
-    smax_y[@]:=max(smax_y[@], ypart r_ilb[@].c+r_ilb[@].hg);
+    nfr_max_x[@]:=xpart r_ilb[@].r;
+    sub_min_y[@]:=min(sub_min_y[@], ypart r_ilb[@].c+r_ilb[@].dp);
+    sub_max_y[@]:=max(sub_max_y[@], ypart r_ilb[@].c+r_ilb[@].hg);
   fi
   %
   % phantom steps
   %
   if known tgt[@]:
-    save phm_pth, phm_pct;
-    path phm_pth;
+    save bot_y, top_y, phm_pct;
+    numeric bot_y, top_y;
     picture phm_pct;
-    save top_y, mid_y, bot_y;
-    numeric top_y, bot_y;
     if drv_bot_roots:
       bot_y:=xpart minmax_y[@]+min_clr_scl*min_clr[drv_sty]/2;
       top_y:=xpart minmax_y[tgt[@]];
@@ -1665,85 +1635,78 @@ vardef drv_build_root[]=
       bot_y:=ypart minmax_y[tgt[@]];
       top_y:=ypart minmax_y[@]-min_clr_scl*min_clr[drv_sty]/2;
     fi
-    mid_y:=(top_y+bot_y)/2;
-    phm_pth:=(0, (bot_y-top_y)/2)--(0, (top_y-bot_y)/2);
-    phm_pct:=phm_pth drv_styled phm_sty[@];
+    phm_pct:=((0, (bot_y-top_y)/2)--(0, (top_y-bot_y)/2))
+      drv_styled phm_sty[@];
     box_init phm[@] (phm_pct shifted ((width phm_pct)/2, 0));
-    phm[@].c=(xpart jdg[@].c, mid_y);
-    imin_x[@]:=min(imin_x[@], xpart phm[@].l);
-    imax_x[@]:=max(imax_x[@], xpart phm[@].r);
+    phm[@].c=(xpart jdg[@].c, (top_y+bot_y)/2);
+    nfr_min_x[@]:=min(nfr_min_x[@], xpart phm[@].l);
+    nfr_max_x[@]:=max(nfr_max_x[@], xpart phm[@].r);
     %
     % phantom steps labels
     %
     if known l_plb[@]:
       l_plb[@].r=phm[@].l shifted (-plb_skp[drv_sty], 0);
-      imin_x[@]:=min(imin_x[@], xpart l_plb[@].l);
+      nfr_min_x[@]:=min(nfr_min_x[@], xpart l_plb[@].l);
     fi
     if known r_plb[@]:
       r_plb[@].l=phm[@].r shifted ( plb_skp[drv_sty], 0);
-      imax_x[@]:=max(imax_x[@], xpart r_plb[@].r);
+      nfr_max_x[@]:=max(nfr_max_x[@], xpart r_plb[@].r);
     fi
   fi
   %
-  % smin_x & smax_x
+  % sub_min_x & sub_max_x
   %
-  smin_x[@]:=imin_x[@];
-  smax_x[@]:=imax_x[@];
+  sub_min_x[@]:=nfr_min_x[@];
+  sub_max_x[@]:=nfr_max_x[@];
   for prm_rnk=0 upto prm_num[@]-1:
-    smin_x[@]:=min(smin_x[@], smin_x[prm[@][prm_rnk]]);
-    smax_x[@]:=max(smax_x[@], smax_x[prm[@][prm_rnk]]);
+    sub_min_x[@]:=min(sub_min_x[@], sub_min_x[prm[@][prm_rnk]]);
+    sub_max_x[@]:=max(sub_max_x[@], sub_max_x[prm[@][prm_rnk]]);
   endfor
   %
   % delimiters
   %
   if known l_dlb[@] or known r_dlb[@]:
-    save idx, mmy, min_y, max_y;
-    numeric idx, min_y, max_y;
+    save mmy, min_y, max_y;
+    numeric min_y, max_y;
     pair mmy;
     mmy:=minmax_y[@];
     min_y:=xpart mmy;
     max_y:=ypart mmy;
     if known l_dlb[@]:
       box_init l_dlm[@] (delim l (max_y-min_y));
-      l_dlm[@].r=(smin_x[@], (max_y+min_y)/2);
+      l_dlm[@].r=(sub_min_x[@], (max_y+min_y)/2);
       l_dlb[@].r=l_dlm[@].l;
-      smin_x[@]:=xpart l_dlb[@].l;
+      sub_min_x[@]:=xpart l_dlb[@].l;
     fi
     if known r_dlb[@]:
       box_init r_dlm[@] (delim r (max_y-min_y));
-      r_dlm[@].l=(smax_x[@], (max_y+min_y)/2);
+      r_dlm[@].l=(sub_max_x[@], (max_y+min_y)/2);
       r_dlb[@].l=r_dlm[@].r;
-      smax_x[@]:=xpart r_dlb[@].r;
+      sub_max_x[@]:=xpart r_dlb[@].r;
     fi
   fi
   if (known l_dlb[@]) or boxed[@]:
+    save idx;
+    numeric idx;
     idx:=@;
     forever:
-      imin_x[idx]:=smin_x[@];
+      nfr_min_x[idx]:=sub_min_x[@];
       exitif unknown l_prm[idx];
       idx:=l_prm[idx];
     endfor
   fi
   if (known r_dlb[@]) or boxed[@]:
+    save idx;
+    numeric idx;
     idx:=@;
     forever:
-      imax_x[idx]:=smax_x[@];
+      nfr_max_x[idx]:=sub_max_x[@];
       exitif unknown r_prm[idx];
       idx:=r_prm[idx];
     endfor
   fi
 enddef;
 
-vardef drv_build=
-  if not drv_checked:
-    drv_check;
-  fi
-  for idx=0 upto root_num-1:
-    drv_build_root[root[idx]];
-  endfor
-  drv_built:=true;
-enddef;
-
 %
 % Freezing
 %
@@ -1766,28 +1729,31 @@ vardef drv_freeze_root[]=
 enddef;
 
 vardef drv_freeze=
-  if not drv_built:
-    drv_build;
+  if not drv_checked:
+    drv_check;
   fi
   save root_idx;
   numeric root_idx;
-  root_idx:=root[0];
-  if unknown iln[root_idx].c:
-    %
-    % default math axis
-    %
-    if drv_axis_ref="iln":
-      iln[root_idx].c=(0, axis_hg[drv_sty]);
-    else: % drv_axis_ref="jdg"
-      jdg[root_idx].c=(0, axis_hg[drv_sty]);
+  for root_rnk=0 upto root_num-1:
+    root_idx:=root[root_rnk];
+    drv_build_root[root_idx];
+    if unknown xpart jdg[root_idx].c:
+      if root_rnk=0:
+        xpart jdg[root_idx].c=0;
+      else:
+        sub_min_x[root_idx]=sub_max_x[root[root_rnk-1]]
+          +prm_skp_scl*prm_skp[drv_sty];
+      fi
     fi
-    drv_freeze_root[root_idx];
-  fi
-  for idx=1 upto root_num-1:
-    root_idx:=root[idx];
-    if unknown iln[root_idx].c:
-      smin_x[root_idx]=smax_x[root[idx-1]]+prm_skp_scl*prm_skp[drv_sty];
-      ypart iln[root_idx].c=ypart iln[root[idx-1]].c;
+    if unknown ypart jdg[root_idx].c:
+      %
+      % default math axis
+      %
+      if drv_axis_ref="iln":
+        ypart iln[root_idx].c=axis_hg[drv_sty];
+      else: % drv_axis_ref="jdg"
+        ypart jdg[root_idx].c=axis_hg[drv_sty];
+      fi
     fi
     drv_freeze_root[root_idx];
   endfor
@@ -1892,12 +1858,12 @@ vardef drv_tree=
   if not drv_frozen:
     drv_freeze;
   fi
-  for root_idx=0 upto root_num-1:
+  for root_rnk=0 upto root_num-1:
     if drv_proofmode_on:
-      drv_tree_addto pct (root[root_idx]) withcolor prf_clr;
-      prf_tree_addto pct (root[root_idx]);
+      drv_tree_addto pct (root[root_rnk]) withcolor prf_clr;
+      prf_tree_addto pct (root[root_rnk]);
     else:
-      drv_tree_addto pct (root[root_idx]);
+      drv_tree_addto pct (root[root_rnk]);
     fi
   endfor
   pct
@@ -1914,13 +1880,13 @@ vardef drv_bbox[]=
     if known l_dlm[@].r:
       xpart l_dlm[@].r
     else:
-      smin_x[@]
+      sub_min_x[@]
     fi-jdg_skp_scl*jdg_skp[jdg_sty[drv_sty]];
   max_x:=
     if known r_dlm[@].l:
       xpart l_dlm[@].l
     else:
-      smax_x[@]
+      sub_max_x[@]
     fi+jdg_skp_scl*jdg_skp[jdg_sty[drv_sty]];
   mmy:=minmax_y[@];
   min_y:=xpart mmy;
@@ -2158,7 +2124,8 @@ vardef drv_axis_reference suffix ref_sfx=
   string ref_str;
   ref_str:=str ref_sfx;
   if (ref_str<>"iln") and (ref_str<>"jdg"):
-    drv_errhelp "Valid identifiers are iln (inference line axis) and"&
+    drv_errhelp "Valid identifiers are"&
+      " iln (inference line axis) and"&
       " jdg (judgment math-axis).";
     drv_errmessage (ref_str&" is not a valid reference identifier");
   else:
@@ -2168,9 +2135,9 @@ enddef;
 
 vardef drv_delimiter (suffix pos_sfx) (expr dlm_str)=
   if check_position_left (pos_sfx, true):
-    drv_l_dlm:=dlm_str;
+    drv_ldlm_str:=dlm_str;
   else:
-    drv_r_dlm:=dlm_str;
+    drv_rdlm_str:=dlm_str;
   fi
 enddef;
 
diff --git a/Master/texmf-dist/doc/metapost/drv/drv-guide.pdf b/Master/texmf-dist/doc/metapost/drv/drv-guide.pdf
index ab7d917ba9e..8b1cf44c736 100644
--- a/Master/texmf-dist/doc/metapost/drv/drv-guide.pdf
+++ b/Master/texmf-dist/doc/metapost/drv/drv-guide.pdf
diff --git a/Master/texmf-dist/doc/metapost/drv/sample/coq-sample.mp b/Master/texmf-dist/doc/metapost/drv/sample/coq-sample.mp
index c10dc3972c4..31a25a22a63 100644
--- a/Master/texmf-dist/doc/metapost/drv/sample/coq-sample.mp
+++ b/Master/texmf-dist/doc/metapost/drv/sample/coq-sample.mp
@@ -39,7 +39,7 @@ for index=0 upto 6:
           nfr 7 () ("\var", 1);
   setbounds currentpicture to drv_bbox 0;
     % All the pictures will have the same bounding box
-    % as the complete derivation tree.
+    % as the full derivation tree.
   draw sbj[0][0];
   if index=0:
     draw sbj[0][1] withcolor blue;
diff --git a/Master/texmf-dist/doc/metapost/drv/sample/drv.mp b/Master/texmf-dist/doc/metapost/drv/sample/drv.mp
index 5eb38396144..69f2f9f72c7 100644
--- a/Master/texmf-dist/doc/metapost/drv/sample/drv.mp
+++ b/Master/texmf-dist/doc/metapost/drv/sample/drv.mp
@@ -1,4 +1,4 @@
-%% drv.mp 0.93
+%% drv.mp 0.94
 %% Copyright 2009 Laurent M\'ehats
 %
 % This work may be distributed and/or modified under the
@@ -188,10 +188,10 @@
 %
 %   drv_left_delimiter <str>
 %	<str>		left delimiter math-mode LaTeX code
-%			  "("	$($
-%			  "["	$[$
-%			  "\lbrace"	$\lbrace$
-%			  "\langle"	$\langle$
+%			  "("
+%			  "["
+%			  "\lbrace"
+%			  "\langle"
 %			  etc.
 %
 %   drv_right_delimiter <str>
@@ -391,8 +391,8 @@ drv_message "done.";
 % writing LaTeX picture definitions
 %
 
-numeric tex_pct_idx;
-tex_pct_idx:=0;
+numeric tex_pct_rnk;
+tex_pct_rnk:=0;
 
 % Math style indices: 0, 1, 2, 3
 string mth_sty_str[];
@@ -410,14 +410,14 @@ vardef drv_tex[] expr tex_str=
   string def_str;
   picture pct;
   def_str:="btex{"&drv_fontsize&"$"&mth_sty_str[@]&"{}"&tex_str&"{}$}etex;";
-  write "tex_pct["&(decimal tex_pct_idx)&"]:="&def_str to delayed_tex_file;
+  write "tex_pct["&(decimal tex_pct_rnk)&"]:="&def_str to delayed_tex_file;
   pct:=
-    if known tex_pct[tex_pct_idx]:
-      tex_pct[tex_pct_idx]
+    if known tex_pct[tex_pct_rnk]:
+      tex_pct[tex_pct_rnk]
     else:
       nullpicture
     fi;
-  tex_pct_idx:=tex_pct_idx+1;
+  tex_pct_rnk:=tex_pct_rnk+1;
   pct
 enddef;
 
@@ -644,31 +644,31 @@ vardef drv_beginfig=
   numeric iln_sty[];
   numeric l_prm[], r_prm[];
   %
-  % imin_x[i]	inference minimal x
-  % l_dlb[i]	left delimiter label drv-box
-  % l_dlm[i]	left delimiter drv-box
-  % l_ilb[i]	left label drv-box
-  % iln[i]	inference line drv-box
-  % r_ilb[i]	right label drv-box
-  % r_dlm[i]	right delimiter drv-box
-  % r_dlb[i]	right delimiter label drv-box
-  % imax_x[i]	inference maximal x
+  % nfr_min_x[i]	inference minimal x
+  % l_dlb[i]		left delimiter label drv-box
+  % l_dlm[i]		left delimiter drv-box
+  % l_ilb[i]		left label drv-box
+  % iln[i]		inference line drv-box
+  % r_ilb[i]		right label drv-box
+  % r_dlm[i]		right delimiter drv-box
+  % r_dlb[i]		right delimiter label drv-box
+  % nfr_max_x[i]	inference maximal x
   %
-  numeric imin_x[];
+  numeric nfr_min_x[];
   drv_box "l_dlb[]", "l_dlm[]", "l_ilb[]";
   drv_box "iln[]";
   drv_box "r_ilb[]", "r_dlm[]", "r_dlb[]";
-  numeric imax_x[];
+  numeric nfr_max_x[];
   %
   % Sub-trees
   %
-  % smin_x[i]	sub-tree minimal x
-  % smax_x[i]	sub-tree maximal x
-  % smin_y[i]	sub-tree minimal y
-  % smax_y[i]	sub-tree maximal y
-  % boxed[i]	boolean
+  % sub_min_x[i]	sub-tree minimal x
+  % sub_max_x[i]	sub-tree maximal x
+  % sub_min_y[i]	sub-tree minimal y
+  % sub_max_y[i]	sub-tree maximal y
+  % boxed[i]		boolean
   %
-  numeric smin_x[], smax_x[], smin_y[], smax_y[];
+  numeric sub_min_x[], sub_max_x[], sub_min_y[], sub_max_y[];
   boolean boxed[];
   %
   % Pen initialization
@@ -694,14 +694,13 @@ vardef drv_beginfig=
   %
   % root_num	number of roots
   % root[i]	root index (i ranges from 0 to root_num-1)
-  % drv_built	boolean
+  % drv_checked	boolean
   % drv_frozen	boolean
   %
   numeric root_num, root[];
-  boolean drv_checked, drv_built, drv_frozen;
+  boolean drv_checked, drv_frozen;
   root_num:=0;
   drv_checked:=false;
-  drv_built:=false;
   drv_frozen:=false;
   %
   % Phantom steps
@@ -819,27 +818,19 @@ vardef jgm[] text SUB=
     jdg_wd:=0;
     sbj_rnk:=0;
     for sub=SUB:
-      sbj_pct:=
-        if picture sub:
-          sub
-        elseif sub<>"":
-          mth_tex[jdg_sty[drv_sty]] sub
-        else:
-          nullpicture
-        fi;
+      sbj_pct:=mth_tex[jdg_sty[drv_sty]] sub;
       box_init sbj[@][sbj_rnk] (sbj_pct);
-      if sbj_rnk>0:
-        sbj[@][sbj_rnk-1].r=sbj[@][sbj_rnk].l;
+      if sbj_rnk>0:				% non mandatory test
+        sbj[@][sbj_rnk-1].r=sbj[@][sbj_rnk].l;	% irrelevant if rnk=0
       fi
       addto jdg_pct also sbj_pct shifted (jdg_wd, 0);
-      jdg_wd:=width jdg_pct;
+      jdg_wd:=jdg_wd+width sbj_pct;
       sbj_rnk:=sbj_rnk+1;
     endfor
     sbj_num[@]:=sbj_rnk;
     box_init jdg[@] (jdg_pct);
-    if sbj_num[@]>0:
-      jdg[@].l=sbj[@][0].l;
-      jdg[@].r=sbj[@][sbj_num[@]-1].r;
+    if sbj_num[@]>0:				% non mandatory test
+      jdg[@].l=sbj[@][0].l;			% irrelevant if sbj_num=0
     fi
   fi
 enddef;
@@ -850,6 +841,19 @@ enddef;
 % Inference declarations
 %
 
+%
+% 1. Global parameters
+%
+
+numeric drv_jct_sty;	% default junction style
+string  drv_alg_sty;	% default junction style
+numeric drv_iln_sty;	% default inference line path-style
+numeric drv_phm_sty;	% default phantom steps path-style
+
+%
+% 2. Macros
+%
+
 vardef check_junction_style (suffix sty_sfx) (expr default)=
   save sty_str;
   string sty_str;
@@ -931,13 +935,9 @@ vardef check_path_style (suffix sty_sfx) (expr default)=
   fi
 enddef;
 
-vardef opt_init[] @# expr arg=
-  if picture arg:
-    if arg<>nullpicture:
-      box_init @# (arg);
-    fi
-  elseif arg<>"":
-    box_init @# (mth_tex[@] arg);
+vardef opt_init[] @# expr str=
+  if str<>"":
+    box_init @# (mth_tex[@] str);
   fi
 enddef;
 
@@ -971,17 +971,17 @@ vardef NFR[] (text PRM) (expr lilb, rilb, ldlb, rdlb)
           %
           % roots list update
           %
-          save root_idx;
-          numeric root_idx;
-          root_idx:=0;
+          save root_rnk;
+          numeric root_rnk;
+          root_rnk:=0;
           forever:
-            exitif root[root_idx]=prm_idx;
-            root_idx:=root_idx+1;
+            exitif root[root_rnk]=prm_idx;
+            root_rnk:=root_rnk+1;
           endfor
           forever:
-            exitif root_idx=root_num-1;
-            root[root_idx]:=root[root_idx+1];
-            root_idx:=root_idx+1;
+            exitif root_rnk=root_num-1;
+            root[root_rnk]:=root[root_rnk+1];
+            root_rnk:=root_rnk+1;
           endfor
           root_num:=root_num-1;
         fi
@@ -1033,9 +1033,6 @@ vardef NFR[] (text PRM) (expr lilb, rilb, ldlb, rdlb)
     jct_sty[@]:=check_junction_style (j_sty, drv_jct_sty);
     alg_sty[@]:=check_alignment_style (a_sty, drv_alg_sty);
     iln_sty[@]:=check_path_style (i_sty, drv_iln_sty);
-    if drv_boxmode_on:
-      boxed[@]:=true;
-    fi
   fi
 enddef;
 
@@ -1051,23 +1048,23 @@ vardef MVD[] (expr inf_num, lplb, rplb) (suffix a_sty, p_sty)=
     drv_errmessage (decimal inf_num)&" is not a valid number of inference"&
       " steps";
   else:
-    save aux_idx, aux_sty, phm_jdg;
-    numeric aux_idx, aux_sty;
+    save prm_idx, pth_sty, phm_jdg;
+    numeric prm_idx, pth_sty;
     picture phm_jdg;
-    aux_sty:=check_path_style (p_sty, drv_phm_sty);
+    pth_sty:=check_path_style (p_sty, drv_phm_sty);
     phm_jdg:=nullpicture;
-    setbounds phm_jdg to (0, 0)--(iln_hg[aux_sty]-iln_dp[aux_sty], 0)--cycle;
-    aux_idx:=@;
+    setbounds phm_jdg to (0, 0)--(iln_hg[pth_sty]-iln_dp[pth_sty], 0)--cycle;
+    prm_idx:=@;
     for i=1 upto inf_num:
       phm_idx:=phm_idx-1;
       box_init jdg[phm_idx] (phm_jdg);
       sbj_num[phm_idx]:=0;
-      NFR[phm_idx] (aux_idx) ("", "", "", "", 0, a_sty, 0);
-      aux_idx:=phm_idx;
+      NFR[phm_idx] (prm_idx) ("", "", "", "", 0, a_sty, 0);
+      prm_idx:=phm_idx;
     endfor
     src[@]:=phm_idx;
     tgt[phm_idx]:=@;
-    phm_sty[phm_idx]:=aux_sty;
+    phm_sty[phm_idx]:=pth_sty;
     %
     % lplb, rplb: phantom steps labels
     %
@@ -1086,33 +1083,20 @@ enddef;
 % Optional labels & shorthands
 %
 
-numeric drv_jct_sty;	% default junction style
-string  drv_alg_sty;	% default junction style
-numeric drv_iln_sty;	% default inference line path-style
-numeric drv_phm_sty;	% default phantom steps path-style
-
 boolean drv_left_ilb;	% inference labels on the left
 boolean drv_left_dlb;	% delimiter labels (hence delimiters) on the left
 boolean drv_left_plb;	% phantom steps labels on the left
 
-vardef arg_type expr arg=
-  if picture arg:
-    "picture"
-  else:
-    "string"
-  fi
-enddef;
-
 vardef opt_lbls @# (text LBL) expr left_lbls=
   save lbl_num, fst_lbl, snd_lbl;
   numeric lbl_num;
   lbl_num:=0;
   for lbl=LBL:
     if lbl_num=0:
-      scantokens (arg_type lbl) fst_lbl;
+      string fst_lbl;
       fst_lbl:=lbl;
     elseif lbl_num=1:
-      scantokens (arg_type lbl) snd_lbl;
+      string snd_lbl;
       snd_lbl:=lbl;
     else:
       drv_errhelp "At most two labels can be specified:"&
@@ -1121,26 +1105,20 @@ vardef opt_lbls @# (text LBL) expr left_lbls=
     fi
     lbl_num:=lbl_num+1;
   endfor
+  string @#.l;
+  string @#.r;
   if lbl_num=0:
-    string @#.l;
-    string @#.r;
     @#.l:="";
     @#.r:="";
   elseif lbl_num=1:
     if left_lbls:
-      scantokens (arg_type fst_lbl) @#.l;
-      string @#.r;
       @#.l:=fst_lbl;
       @#.r:="";
     else:
-      string @#.l;
-      scantokens (arg_type fst_lbl) @#.r;
       @#.l:="";
       @#.r:=fst_lbl;
     fi
   else:
-    scantokens (arg_type fst_lbl) @#.l;
-    scantokens (arg_type snd_lbl) @#.r;
     @#.l:=fst_lbl;
     @#.r:=snd_lbl;
   fi
@@ -1339,8 +1317,8 @@ enddef;
 % 1. Global parameters
 %
 
-string drv_l_dlm; % left delimiter LaTeX code
-string drv_r_dlm; % right delimiter LaTeX code
+string drv_ldlm_str; % left delimiter LaTeX code
+string drv_rdlm_str; % right delimiter LaTeX code
 
 %
 % 2. Macros
@@ -1352,16 +1330,16 @@ vardef minmax_y[]=(
       ypart jdg[@].c-num_hg+iln_hg[(iln_sty[ccl[@]])]
         +min_clr_scl*min_clr[drv_sty]/2
     else:
-      smin_y[@]-min_clr_scl*min_clr[drv_sty]
+      sub_min_y[@]-min_clr_scl*min_clr[drv_sty]
     fi,
-    smax_y[@]+min_clr_scl*min_clr[drv_sty]
+    sub_max_y[@]+min_clr_scl*min_clr[drv_sty]
   else:
-    smin_y[@]-min_clr_scl*min_clr[drv_sty],
+    sub_min_y[@]-min_clr_scl*min_clr[drv_sty],
     if known ccl[@]:
-      ypart jdg[@].c-den_dp-iln_hg[(iln_sty[ccl[@]])]
+      ypart jdg[@].c-den_dp+iln_dp[(iln_sty[ccl[@]])]
         -min_clr_scl*min_clr[drv_sty]/2
     else:
-      smax_y[@]+min_clr_scl*min_clr[drv_sty]
+      sub_max_y[@]+min_clr_scl*min_clr[drv_sty]
     fi
   fi)
 enddef;
@@ -1374,9 +1352,9 @@ vardef delim @# expr dlm_len=
   rule_str:="\rule{0bp}{"&(decimal(dlm_len/2+axis_hg[drv_sty]))&"bp}";
   dlm_str:=
     if str @#="l":
-      "\left"&drv_l_dlm&rule_str&"\right."
+      "\left"&drv_ldlm_str&rule_str&"\right."
     else:
-      "\left."&rule_str&"\right"&drv_r_dlm
+      "\left."&rule_str&"\right"&drv_rdlm_str
     fi;
   dlm_pct:=mth_tex[drv_sty] dlm_str;
   dlm_dp:=depth dlm_pct;
@@ -1472,7 +1450,7 @@ vardef drv_check_root[]=
       fi
     fi
     if unknown boxed[@]:
-      boxed[@]:=false;
+      boxed[@]:=drv_boxmode_on;
     fi
   fi
 enddef;
@@ -1490,8 +1468,8 @@ vardef drv_check=
       save root_str;
       string root_str;
       root_str:=decimal root_idx;
-      for idx=1 upto root_num-1:
-        root_idx:=root[idx];
+      for root_rnk=1 upto root_num-1:
+        root_idx:=root[root_rnk];
         drv_check_root[root_idx];
         root_str:=root_str&", "&(decimal root_idx);
       endfor
@@ -1507,70 +1485,96 @@ enddef;
 
 vardef drv_build_root[]=
   %
+  % orientation
+  %
+  if drv_bot_roots:
+    ypart iln[@].c=ypart jdg[@].c-den_dp;
+    sub_min_y[@]:=ypart jdg[@].c+jdg[@].dp;
+    sub_max_y[@]:=
+      if iln_sty[@]=0:
+        ypart jdg[@].c+jdg[@].hg
+      else:
+        ypart iln[@].c+iln_hg[iln_sty[@]]
+      fi;
+    for prm_rnk=0 upto prm_num[@]-1:
+      ypart jdg[prm[@][prm_rnk]].c=ypart iln[@].c+num_hg;
+      drv_build_root[prm[@][prm_rnk]];
+      sub_max_y[@]:=max(sub_max_y[@], sub_max_y[prm[@][prm_rnk]]);
+    endfor
+  else:
+    ypart iln[@].c=ypart jdg[@].c-num_hg;
+    sub_min_y[@]:=
+      if iln_sty[@]=0:
+        ypart jdg[@].c+jdg[@].dp
+      else:
+        ypart iln[@].c+iln_dp[iln_sty[@]]
+      fi;
+    sub_max_y[@]:=ypart jdg[@].c+jdg[@].hg;
+    for prm_rnk=0 upto prm_num[@]-1:
+      ypart jdg[prm[@][prm_rnk]].c=ypart iln[@].c+den_dp;
+      drv_build_root[prm[@][prm_rnk]];
+      sub_min_y[@]:=min(sub_min_y[@], sub_min_y[prm[@][prm_rnk]]);
+    endfor
+  fi
+  %
   % premises junction (from left to right)
   %
-  for prm_rnk=0 upto  prm_num[@]-1:
-    drv_build_root[prm[@][prm_rnk]];
-    if prm_rnk>0:
-      save ll_idx, lr_idx, rl_idx, rr_idx;
-      save lmax_x, rmin_x, min_skp;
-      numeric ll_idx, lr_idx, rl_idx, rr_idx;
-      numeric lmax_x, rmin_x, min_skp;
-      ypart jdg[prm[@][prm_rnk-1]].c=ypart jdg[prm[@][prm_rnk]].c;
-      ll_idx:=prm[@][0];
-      lr_idx:=prm[@][prm_rnk-1];
-      rl_idx:=prm[@][prm_rnk];
-      rr_idx:=prm[@][prm_rnk];
-      lmax_x:=imax_x[lr_idx];
-      rmin_x:=imin_x[rl_idx];
-      min_skp[0]:=rmin_x-lmax_x;
-      forever:
-        exitif (unknown r_prm[lr_idx]) or (unknown l_prm[rl_idx]);
-        ll_idx:=l_prm[ll_idx];
-        lr_idx:=r_prm[lr_idx];
-        rl_idx:=l_prm[rl_idx];
-        rr_idx:=r_prm[rr_idx];
-        lmax_x:=max(lmax_x, imax_x[lr_idx]);
-        rmin_x:=min(rmin_x, imin_x[rl_idx]);
-        min_skp[0]:=min(min_skp[0], imin_x[rl_idx]-imax_x[lr_idx]);
-      endfor
-      min_skp[1]:=rmin_x-lmax_x;
-      if known r_prm[lr_idx]:
-        r_prm[rr_idx]:= r_prm[lr_idx];
-        lmax_x:=smax_x[lr_idx];
-      elseif known l_prm[rl_idx]:
-        l_prm[ll_idx]:=l_prm[rl_idx];
-        rmin_x:=smin_x[rl_idx];
-      fi
-      min_skp[2]:=rmin_x-lmax_x;
-      if jct_sty[@]<3:
-        min_skp[jct_sty[@]]=prm_skp_scl*prm_skp[drv_sty];
-      fi
+  for prm_rnk=1 upto  prm_num[@]-1:
+    save l_lmost, l_rmost, r_lmost, r_rmost;
+    save l_max_x, r_min_x, min_skp;
+    numeric l_lmost, l_rmost, r_lmost, r_rmost;
+    numeric l_max_x, r_min_x, min_skp[];
+    l_lmost:=prm[@][0];
+    l_rmost:=prm[@][prm_rnk-1];
+    r_lmost:=prm[@][prm_rnk];
+    r_rmost:=prm[@][prm_rnk];
+    l_max_x:=nfr_max_x[l_rmost];
+    r_min_x:=nfr_min_x[r_lmost];
+    min_skp[0]:=r_min_x-l_max_x;
+    forever:
+      exitif (unknown r_prm[l_rmost]) or (unknown l_prm[r_lmost]);
+      l_lmost:=l_prm[l_lmost];
+      l_rmost:=r_prm[l_rmost];
+      r_lmost:=l_prm[r_lmost];
+      r_rmost:=r_prm[r_rmost];
+      l_max_x:=max(l_max_x, nfr_max_x[l_rmost]);
+      r_min_x:=min(r_min_x, nfr_min_x[r_lmost]);
+      min_skp[0]:=min(min_skp[0], nfr_min_x[r_lmost]-nfr_max_x[l_rmost]);
+    endfor
+    min_skp[1]:=r_min_x-l_max_x;
+    if known r_prm[l_rmost]:
+      r_prm[r_rmost]:= r_prm[l_rmost];
+      l_max_x:=sub_max_x[l_rmost];
+    elseif known l_prm[r_lmost]:
+      l_prm[l_lmost]:=l_prm[r_lmost];
+      r_min_x:=sub_min_x[r_lmost];
+    fi
+    min_skp[2]:=r_min_x-l_max_x;
+    if jct_sty[@]<3:
+      min_skp[jct_sty[@]]=prm_skp_scl*prm_skp[drv_sty];
     fi
   endfor
-  if  prm_num[@]>0:
-    l_prm[@]:=prm[@][0];
-    r_prm[@]:=prm[@][prm_num[@]-1];
-  fi
   %
   % judgment alignment
   %
   if prm_num[@]=0:
-    imin_x[@]:=xpart jdg[@].l-jdg_skp_scl*jdg_skp[jdg_sty[drv_sty]];
-    imax_x[@]:=xpart jdg[@].r+jdg_skp_scl*jdg_skp[jdg_sty[drv_sty]];
+    nfr_min_x[@]:=xpart jdg[@].l;
+    nfr_max_x[@]:=xpart jdg[@].r;
   else:
+    l_prm[@]:=prm[@][0];
+    r_prm[@]:=prm[@][prm_num[@]-1];
     save l_xref, r_xref;
     l_xref=
-      if boxed[prm[@][0]]:
-        smin_x[prm[@][0]]
+      if boxed[l_prm[@]]:
+        sub_min_x[l_prm[@]]
       else:
-        xpart jdg[prm[@][0]].l
+        xpart jdg[l_prm[@]].l
       fi;
     r_xref=
-      if boxed[prm[@][prm_num[@]-1]]:
-        smax_x[prm[@][prm_num[@]-1]]
+      if boxed[r_prm[@]]:
+        sub_max_x[r_prm[@]]
       else:
-        xpart jdg[prm[@][prm_num[@]-1]].r
+        xpart jdg[r_prm[@]].r
       fi;
     if alg_sty[@]="l":
       xpart jdg[@].l=l_xref;
@@ -1579,10 +1583,8 @@ vardef drv_build_root[]=
     elseif alg_sty[@]="r":
       xpart jdg[@].r=r_xref;
     fi
-    imin_x[@]:=min(xpart jdg[@].l, l_xref)
-          -jdg_skp_scl*jdg_skp[jdg_sty[drv_sty]];
-    imax_x[@]:=max(xpart jdg[@].r, r_xref)
-          +jdg_skp_scl*jdg_skp[jdg_sty[drv_sty]];
+    nfr_min_x[@]:=min(xpart jdg[@].l, l_xref);
+    nfr_max_x[@]:=max(xpart jdg[@].r, r_xref);
   fi
   %
   % inference line
@@ -1590,7 +1592,7 @@ vardef drv_build_root[]=
   save iln_wd, iln_pct;
   numeric iln_wd;
   picture iln_pct;
-  iln_wd:=imax_x[@]-imin_x[@];
+  iln_wd:=nfr_max_x[@]-nfr_min_x[@]+2*jdg_skp_scl*jdg_skp[jdg_sty[drv_sty]];
   iln_pct:=((0, 0)--(iln_wd, 0)) drv_styled iln_sty[@];
   setbounds iln_pct to
     (0, ypart llcorner iln_pct)
@@ -1599,65 +1601,33 @@ vardef drv_build_root[]=
   --(iln_wd, ypart llcorner iln_pct)
   --cycle; % ! `linecap:=butt' and `linecap:=squared' -> same bounding box !
   box_init iln[@] (iln_pct);
-  xpart iln[@].c=(imin_x[@]+imax_x[@])/2;
-  %
-  % orientation, smin_y & smax_y
-  %
-  if drv_bot_roots:
-    ypart iln[@].c=ypart jdg[@].c-den_dp;
-    smin_y[@]:=ypart jdg[@].c+jdg[@].dp;
-    smax_y[@]:=
-      if iln_sty[@]=0:
-        ypart jdg[@].c+jdg[@].hg
-      else:
-        ypart iln[@].c+iln[@].hg
-      fi;
-    if prm_num[@]>0:
-      ypart iln[@].c=ypart jdg[prm[@][0]].c-num_hg;
-      for prm_rnk=0 upto prm_num[@]-1:
-        smax_y[@]:=max(smax_y[@], smax_y[prm[@][prm_rnk]]);
-      endfor;
-    fi
-  else:
-    ypart iln[@].c=ypart jdg[@].c-num_hg;
-    smin_y[@]:=
-      if iln_sty[@]=0:
-        ypart jdg[@].c+jdg[@].dp
-      else:
-        ypart iln[@].c+iln[@].dp
-      fi;
-    smax_y[@]:=ypart jdg[@].c+jdg[@].hg;
-    if prm_num[@]>0:
-      ypart iln[@].c=ypart jdg[prm[@][0]].c-den_dp;
-      for prm_rnk=0 upto prm_num[@]-1:
-        smin_y[@]:=min(smin_y[@], smin_y[prm[@][prm_rnk]]);
-      endfor;
-    fi
+  xpart iln[@].c=(nfr_min_x[@]+nfr_max_x[@])/2;
+  if iln_sty[@]>0:
+    nfr_min_x[@]:=xpart iln[@].l;
+    nfr_max_x[@]:=xpart iln[@].r;
   fi
   %
   % inference labels
   %
   if known l_ilb[@]:
     l_ilb[@].r=iln[@].l shifted (-ilb_skp_scl*ilb_skp[drv_sty], 0);
-    imin_x[@]:=xpart l_ilb[@].l;
-    smin_y[@]:=min(smin_y[@], ypart l_ilb[@].c+l_ilb[@].dp);
-    smax_y[@]:=max(smax_y[@], ypart l_ilb[@].c+l_ilb[@].hg);
+    nfr_min_x[@]:=xpart l_ilb[@].l;
+    sub_min_y[@]:=min(sub_min_y[@], ypart l_ilb[@].c+l_ilb[@].dp);
+    sub_max_y[@]:=max(sub_max_y[@], ypart l_ilb[@].c+l_ilb[@].hg);
   fi
   if known r_ilb[@]:
     r_ilb[@].l=iln[@].r shifted (ilb_skp_scl*ilb_skp[drv_sty], 0);
-    imax_x[@]:=xpart r_ilb[@].r;
-    smin_y[@]:=min(smin_y[@], ypart r_ilb[@].c+r_ilb[@].dp);
-    smax_y[@]:=max(smax_y[@], ypart r_ilb[@].c+r_ilb[@].hg);
+    nfr_max_x[@]:=xpart r_ilb[@].r;
+    sub_min_y[@]:=min(sub_min_y[@], ypart r_ilb[@].c+r_ilb[@].dp);
+    sub_max_y[@]:=max(sub_max_y[@], ypart r_ilb[@].c+r_ilb[@].hg);
   fi
   %
   % phantom steps
   %
   if known tgt[@]:
-    save phm_pth, phm_pct;
-    path phm_pth;
+    save bot_y, top_y, phm_pct;
+    numeric bot_y, top_y;
     picture phm_pct;
-    save top_y, mid_y, bot_y;
-    numeric top_y, bot_y;
     if drv_bot_roots:
       bot_y:=xpart minmax_y[@]+min_clr_scl*min_clr[drv_sty]/2;
       top_y:=xpart minmax_y[tgt[@]];
@@ -1665,85 +1635,78 @@ vardef drv_build_root[]=
       bot_y:=ypart minmax_y[tgt[@]];
       top_y:=ypart minmax_y[@]-min_clr_scl*min_clr[drv_sty]/2;
     fi
-    mid_y:=(top_y+bot_y)/2;
-    phm_pth:=(0, (bot_y-top_y)/2)--(0, (top_y-bot_y)/2);
-    phm_pct:=phm_pth drv_styled phm_sty[@];
+    phm_pct:=((0, (bot_y-top_y)/2)--(0, (top_y-bot_y)/2))
+      drv_styled phm_sty[@];
     box_init phm[@] (phm_pct shifted ((width phm_pct)/2, 0));
-    phm[@].c=(xpart jdg[@].c, mid_y);
-    imin_x[@]:=min(imin_x[@], xpart phm[@].l);
-    imax_x[@]:=max(imax_x[@], xpart phm[@].r);
+    phm[@].c=(xpart jdg[@].c, (top_y+bot_y)/2);
+    nfr_min_x[@]:=min(nfr_min_x[@], xpart phm[@].l);
+    nfr_max_x[@]:=max(nfr_max_x[@], xpart phm[@].r);
     %
     % phantom steps labels
     %
     if known l_plb[@]:
       l_plb[@].r=phm[@].l shifted (-plb_skp[drv_sty], 0);
-      imin_x[@]:=min(imin_x[@], xpart l_plb[@].l);
+      nfr_min_x[@]:=min(nfr_min_x[@], xpart l_plb[@].l);
     fi
     if known r_plb[@]:
       r_plb[@].l=phm[@].r shifted ( plb_skp[drv_sty], 0);
-      imax_x[@]:=max(imax_x[@], xpart r_plb[@].r);
+      nfr_max_x[@]:=max(nfr_max_x[@], xpart r_plb[@].r);
     fi
   fi
   %
-  % smin_x & smax_x
+  % sub_min_x & sub_max_x
   %
-  smin_x[@]:=imin_x[@];
-  smax_x[@]:=imax_x[@];
+  sub_min_x[@]:=nfr_min_x[@];
+  sub_max_x[@]:=nfr_max_x[@];
   for prm_rnk=0 upto prm_num[@]-1:
-    smin_x[@]:=min(smin_x[@], smin_x[prm[@][prm_rnk]]);
-    smax_x[@]:=max(smax_x[@], smax_x[prm[@][prm_rnk]]);
+    sub_min_x[@]:=min(sub_min_x[@], sub_min_x[prm[@][prm_rnk]]);
+    sub_max_x[@]:=max(sub_max_x[@], sub_max_x[prm[@][prm_rnk]]);
   endfor
   %
   % delimiters
   %
   if known l_dlb[@] or known r_dlb[@]:
-    save idx, mmy, min_y, max_y;
-    numeric idx, min_y, max_y;
+    save mmy, min_y, max_y;
+    numeric min_y, max_y;
     pair mmy;
     mmy:=minmax_y[@];
     min_y:=xpart mmy;
     max_y:=ypart mmy;
     if known l_dlb[@]:
       box_init l_dlm[@] (delim l (max_y-min_y));
-      l_dlm[@].r=(smin_x[@], (max_y+min_y)/2);
+      l_dlm[@].r=(sub_min_x[@], (max_y+min_y)/2);
       l_dlb[@].r=l_dlm[@].l;
-      smin_x[@]:=xpart l_dlb[@].l;
+      sub_min_x[@]:=xpart l_dlb[@].l;
     fi
     if known r_dlb[@]:
       box_init r_dlm[@] (delim r (max_y-min_y));
-      r_dlm[@].l=(smax_x[@], (max_y+min_y)/2);
+      r_dlm[@].l=(sub_max_x[@], (max_y+min_y)/2);
       r_dlb[@].l=r_dlm[@].r;
-      smax_x[@]:=xpart r_dlb[@].r;
+      sub_max_x[@]:=xpart r_dlb[@].r;
     fi
   fi
   if (known l_dlb[@]) or boxed[@]:
+    save idx;
+    numeric idx;
     idx:=@;
     forever:
-      imin_x[idx]:=smin_x[@];
+      nfr_min_x[idx]:=sub_min_x[@];
       exitif unknown l_prm[idx];
       idx:=l_prm[idx];
     endfor
   fi
   if (known r_dlb[@]) or boxed[@]:
+    save idx;
+    numeric idx;
     idx:=@;
     forever:
-      imax_x[idx]:=smax_x[@];
+      nfr_max_x[idx]:=sub_max_x[@];
       exitif unknown r_prm[idx];
       idx:=r_prm[idx];
     endfor
   fi
 enddef;
 
-vardef drv_build=
-  if not drv_checked:
-    drv_check;
-  fi
-  for idx=0 upto root_num-1:
-    drv_build_root[root[idx]];
-  endfor
-  drv_built:=true;
-enddef;
-
 %
 % Freezing
 %
@@ -1766,28 +1729,31 @@ vardef drv_freeze_root[]=
 enddef;
 
 vardef drv_freeze=
-  if not drv_built:
-    drv_build;
+  if not drv_checked:
+    drv_check;
   fi
   save root_idx;
   numeric root_idx;
-  root_idx:=root[0];
-  if unknown iln[root_idx].c:
-    %
-    % default math axis
-    %
-    if drv_axis_ref="iln":
-      iln[root_idx].c=(0, axis_hg[drv_sty]);
-    else: % drv_axis_ref="jdg"
-      jdg[root_idx].c=(0, axis_hg[drv_sty]);
+  for root_rnk=0 upto root_num-1:
+    root_idx:=root[root_rnk];
+    drv_build_root[root_idx];
+    if unknown xpart jdg[root_idx].c:
+      if root_rnk=0:
+        xpart jdg[root_idx].c=0;
+      else:
+        sub_min_x[root_idx]=sub_max_x[root[root_rnk-1]]
+          +prm_skp_scl*prm_skp[drv_sty];
+      fi
     fi
-    drv_freeze_root[root_idx];
-  fi
-  for idx=1 upto root_num-1:
-    root_idx:=root[idx];
-    if unknown iln[root_idx].c:
-      smin_x[root_idx]=smax_x[root[idx-1]]+prm_skp_scl*prm_skp[drv_sty];
-      ypart iln[root_idx].c=ypart iln[root[idx-1]].c;
+    if unknown ypart jdg[root_idx].c:
+      %
+      % default math axis
+      %
+      if drv_axis_ref="iln":
+        ypart iln[root_idx].c=axis_hg[drv_sty];
+      else: % drv_axis_ref="jdg"
+        ypart jdg[root_idx].c=axis_hg[drv_sty];
+      fi
     fi
     drv_freeze_root[root_idx];
   endfor
@@ -1892,12 +1858,12 @@ vardef drv_tree=
   if not drv_frozen:
     drv_freeze;
   fi
-  for root_idx=0 upto root_num-1:
+  for root_rnk=0 upto root_num-1:
     if drv_proofmode_on:
-      drv_tree_addto pct (root[root_idx]) withcolor prf_clr;
-      prf_tree_addto pct (root[root_idx]);
+      drv_tree_addto pct (root[root_rnk]) withcolor prf_clr;
+      prf_tree_addto pct (root[root_rnk]);
     else:
-      drv_tree_addto pct (root[root_idx]);
+      drv_tree_addto pct (root[root_rnk]);
     fi
   endfor
   pct
@@ -1914,13 +1880,13 @@ vardef drv_bbox[]=
     if known l_dlm[@].r:
       xpart l_dlm[@].r
     else:
-      smin_x[@]
+      sub_min_x[@]
     fi-jdg_skp_scl*jdg_skp[jdg_sty[drv_sty]];
   max_x:=
     if known r_dlm[@].l:
       xpart l_dlm[@].l
     else:
-      smax_x[@]
+      sub_max_x[@]
     fi+jdg_skp_scl*jdg_skp[jdg_sty[drv_sty]];
   mmy:=minmax_y[@];
   min_y:=xpart mmy;
@@ -2158,7 +2124,8 @@ vardef drv_axis_reference suffix ref_sfx=
   string ref_str;
   ref_str:=str ref_sfx;
   if (ref_str<>"iln") and (ref_str<>"jdg"):
-    drv_errhelp "Valid identifiers are iln (inference line axis) and"&
+    drv_errhelp "Valid identifiers are"&
+      " iln (inference line axis) and"&
       " jdg (judgment math-axis).";
     drv_errmessage (ref_str&" is not a valid reference identifier");
   else:
@@ -2168,9 +2135,9 @@ enddef;
 
 vardef drv_delimiter (suffix pos_sfx) (expr dlm_str)=
   if check_position_left (pos_sfx, true):
-    drv_l_dlm:=dlm_str;
+    drv_ldlm_str:=dlm_str;
   else:
-    drv_r_dlm:=dlm_str;
+    drv_rdlm_str:=dlm_str;
   fi
 enddef;
 
diff --git a/Master/texmf-dist/doc/metapost/drv/template/drv.mp b/Master/texmf-dist/doc/metapost/drv/template/drv.mp
index 5eb38396144..69f2f9f72c7 100644
--- a/Master/texmf-dist/doc/metapost/drv/template/drv.mp
+++ b/Master/texmf-dist/doc/metapost/drv/template/drv.mp
@@ -1,4 +1,4 @@
-%% drv.mp 0.93
+%% drv.mp 0.94
 %% Copyright 2009 Laurent M\'ehats
 %
 % This work may be distributed and/or modified under the
@@ -188,10 +188,10 @@
 %
 %   drv_left_delimiter <str>
 %	<str>		left delimiter math-mode LaTeX code
-%			  "("	$($
-%			  "["	$[$
-%			  "\lbrace"	$\lbrace$
-%			  "\langle"	$\langle$
+%			  "("
+%			  "["
+%			  "\lbrace"
+%			  "\langle"
 %			  etc.
 %
 %   drv_right_delimiter <str>
@@ -391,8 +391,8 @@ drv_message "done.";
 % writing LaTeX picture definitions
 %
 
-numeric tex_pct_idx;
-tex_pct_idx:=0;
+numeric tex_pct_rnk;
+tex_pct_rnk:=0;
 
 % Math style indices: 0, 1, 2, 3
 string mth_sty_str[];
@@ -410,14 +410,14 @@ vardef drv_tex[] expr tex_str=
   string def_str;
   picture pct;
   def_str:="btex{"&drv_fontsize&"$"&mth_sty_str[@]&"{}"&tex_str&"{}$}etex;";
-  write "tex_pct["&(decimal tex_pct_idx)&"]:="&def_str to delayed_tex_file;
+  write "tex_pct["&(decimal tex_pct_rnk)&"]:="&def_str to delayed_tex_file;
   pct:=
-    if known tex_pct[tex_pct_idx]:
-      tex_pct[tex_pct_idx]
+    if known tex_pct[tex_pct_rnk]:
+      tex_pct[tex_pct_rnk]
     else:
       nullpicture
     fi;
-  tex_pct_idx:=tex_pct_idx+1;
+  tex_pct_rnk:=tex_pct_rnk+1;
   pct
 enddef;
 
@@ -644,31 +644,31 @@ vardef drv_beginfig=
   numeric iln_sty[];
   numeric l_prm[], r_prm[];
   %
-  % imin_x[i]	inference minimal x
-  % l_dlb[i]	left delimiter label drv-box
-  % l_dlm[i]	left delimiter drv-box
-  % l_ilb[i]	left label drv-box
-  % iln[i]	inference line drv-box
-  % r_ilb[i]	right label drv-box
-  % r_dlm[i]	right delimiter drv-box
-  % r_dlb[i]	right delimiter label drv-box
-  % imax_x[i]	inference maximal x
+  % nfr_min_x[i]	inference minimal x
+  % l_dlb[i]		left delimiter label drv-box
+  % l_dlm[i]		left delimiter drv-box
+  % l_ilb[i]		left label drv-box
+  % iln[i]		inference line drv-box
+  % r_ilb[i]		right label drv-box
+  % r_dlm[i]		right delimiter drv-box
+  % r_dlb[i]		right delimiter label drv-box
+  % nfr_max_x[i]	inference maximal x
   %
-  numeric imin_x[];
+  numeric nfr_min_x[];
   drv_box "l_dlb[]", "l_dlm[]", "l_ilb[]";
   drv_box "iln[]";
   drv_box "r_ilb[]", "r_dlm[]", "r_dlb[]";
-  numeric imax_x[];
+  numeric nfr_max_x[];
   %
   % Sub-trees
   %
-  % smin_x[i]	sub-tree minimal x
-  % smax_x[i]	sub-tree maximal x
-  % smin_y[i]	sub-tree minimal y
-  % smax_y[i]	sub-tree maximal y
-  % boxed[i]	boolean
+  % sub_min_x[i]	sub-tree minimal x
+  % sub_max_x[i]	sub-tree maximal x
+  % sub_min_y[i]	sub-tree minimal y
+  % sub_max_y[i]	sub-tree maximal y
+  % boxed[i]		boolean
   %
-  numeric smin_x[], smax_x[], smin_y[], smax_y[];
+  numeric sub_min_x[], sub_max_x[], sub_min_y[], sub_max_y[];
   boolean boxed[];
   %
   % Pen initialization
@@ -694,14 +694,13 @@ vardef drv_beginfig=
   %
   % root_num	number of roots
   % root[i]	root index (i ranges from 0 to root_num-1)
-  % drv_built	boolean
+  % drv_checked	boolean
   % drv_frozen	boolean
   %
   numeric root_num, root[];
-  boolean drv_checked, drv_built, drv_frozen;
+  boolean drv_checked, drv_frozen;
   root_num:=0;
   drv_checked:=false;
-  drv_built:=false;
   drv_frozen:=false;
   %
   % Phantom steps
@@ -819,27 +818,19 @@ vardef jgm[] text SUB=
     jdg_wd:=0;
     sbj_rnk:=0;
     for sub=SUB:
-      sbj_pct:=
-        if picture sub:
-          sub
-        elseif sub<>"":
-          mth_tex[jdg_sty[drv_sty]] sub
-        else:
-          nullpicture
-        fi;
+      sbj_pct:=mth_tex[jdg_sty[drv_sty]] sub;
       box_init sbj[@][sbj_rnk] (sbj_pct);
-      if sbj_rnk>0:
-        sbj[@][sbj_rnk-1].r=sbj[@][sbj_rnk].l;
+      if sbj_rnk>0:				% non mandatory test
+        sbj[@][sbj_rnk-1].r=sbj[@][sbj_rnk].l;	% irrelevant if rnk=0
       fi
       addto jdg_pct also sbj_pct shifted (jdg_wd, 0);
-      jdg_wd:=width jdg_pct;
+      jdg_wd:=jdg_wd+width sbj_pct;
       sbj_rnk:=sbj_rnk+1;
     endfor
     sbj_num[@]:=sbj_rnk;
     box_init jdg[@] (jdg_pct);
-    if sbj_num[@]>0:
-      jdg[@].l=sbj[@][0].l;
-      jdg[@].r=sbj[@][sbj_num[@]-1].r;
+    if sbj_num[@]>0:				% non mandatory test
+      jdg[@].l=sbj[@][0].l;			% irrelevant if sbj_num=0
     fi
   fi
 enddef;
@@ -850,6 +841,19 @@ enddef;
 % Inference declarations
 %
 
+%
+% 1. Global parameters
+%
+
+numeric drv_jct_sty;	% default junction style
+string  drv_alg_sty;	% default junction style
+numeric drv_iln_sty;	% default inference line path-style
+numeric drv_phm_sty;	% default phantom steps path-style
+
+%
+% 2. Macros
+%
+
 vardef check_junction_style (suffix sty_sfx) (expr default)=
   save sty_str;
   string sty_str;
@@ -931,13 +935,9 @@ vardef check_path_style (suffix sty_sfx) (expr default)=
   fi
 enddef;
 
-vardef opt_init[] @# expr arg=
-  if picture arg:
-    if arg<>nullpicture:
-      box_init @# (arg);
-    fi
-  elseif arg<>"":
-    box_init @# (mth_tex[@] arg);
+vardef opt_init[] @# expr str=
+  if str<>"":
+    box_init @# (mth_tex[@] str);
   fi
 enddef;
 
@@ -971,17 +971,17 @@ vardef NFR[] (text PRM) (expr lilb, rilb, ldlb, rdlb)
           %
           % roots list update
           %
-          save root_idx;
-          numeric root_idx;
-          root_idx:=0;
+          save root_rnk;
+          numeric root_rnk;
+          root_rnk:=0;
           forever:
-            exitif root[root_idx]=prm_idx;
-            root_idx:=root_idx+1;
+            exitif root[root_rnk]=prm_idx;
+            root_rnk:=root_rnk+1;
           endfor
           forever:
-            exitif root_idx=root_num-1;
-            root[root_idx]:=root[root_idx+1];
-            root_idx:=root_idx+1;
+            exitif root_rnk=root_num-1;
+            root[root_rnk]:=root[root_rnk+1];
+            root_rnk:=root_rnk+1;
           endfor
           root_num:=root_num-1;
         fi
@@ -1033,9 +1033,6 @@ vardef NFR[] (text PRM) (expr lilb, rilb, ldlb, rdlb)
     jct_sty[@]:=check_junction_style (j_sty, drv_jct_sty);
     alg_sty[@]:=check_alignment_style (a_sty, drv_alg_sty);
     iln_sty[@]:=check_path_style (i_sty, drv_iln_sty);
-    if drv_boxmode_on:
-      boxed[@]:=true;
-    fi
   fi
 enddef;
 
@@ -1051,23 +1048,23 @@ vardef MVD[] (expr inf_num, lplb, rplb) (suffix a_sty, p_sty)=
     drv_errmessage (decimal inf_num)&" is not a valid number of inference"&
       " steps";
   else:
-    save aux_idx, aux_sty, phm_jdg;
-    numeric aux_idx, aux_sty;
+    save prm_idx, pth_sty, phm_jdg;
+    numeric prm_idx, pth_sty;
     picture phm_jdg;
-    aux_sty:=check_path_style (p_sty, drv_phm_sty);
+    pth_sty:=check_path_style (p_sty, drv_phm_sty);
     phm_jdg:=nullpicture;
-    setbounds phm_jdg to (0, 0)--(iln_hg[aux_sty]-iln_dp[aux_sty], 0)--cycle;
-    aux_idx:=@;
+    setbounds phm_jdg to (0, 0)--(iln_hg[pth_sty]-iln_dp[pth_sty], 0)--cycle;
+    prm_idx:=@;
     for i=1 upto inf_num:
       phm_idx:=phm_idx-1;
       box_init jdg[phm_idx] (phm_jdg);
       sbj_num[phm_idx]:=0;
-      NFR[phm_idx] (aux_idx) ("", "", "", "", 0, a_sty, 0);
-      aux_idx:=phm_idx;
+      NFR[phm_idx] (prm_idx) ("", "", "", "", 0, a_sty, 0);
+      prm_idx:=phm_idx;
     endfor
     src[@]:=phm_idx;
     tgt[phm_idx]:=@;
-    phm_sty[phm_idx]:=aux_sty;
+    phm_sty[phm_idx]:=pth_sty;
     %
     % lplb, rplb: phantom steps labels
     %
@@ -1086,33 +1083,20 @@ enddef;
 % Optional labels & shorthands
 %
 
-numeric drv_jct_sty;	% default junction style
-string  drv_alg_sty;	% default junction style
-numeric drv_iln_sty;	% default inference line path-style
-numeric drv_phm_sty;	% default phantom steps path-style
-
 boolean drv_left_ilb;	% inference labels on the left
 boolean drv_left_dlb;	% delimiter labels (hence delimiters) on the left
 boolean drv_left_plb;	% phantom steps labels on the left
 
-vardef arg_type expr arg=
-  if picture arg:
-    "picture"
-  else:
-    "string"
-  fi
-enddef;
-
 vardef opt_lbls @# (text LBL) expr left_lbls=
   save lbl_num, fst_lbl, snd_lbl;
   numeric lbl_num;
   lbl_num:=0;
   for lbl=LBL:
     if lbl_num=0:
-      scantokens (arg_type lbl) fst_lbl;
+      string fst_lbl;
       fst_lbl:=lbl;
     elseif lbl_num=1:
-      scantokens (arg_type lbl) snd_lbl;
+      string snd_lbl;
       snd_lbl:=lbl;
     else:
       drv_errhelp "At most two labels can be specified:"&
@@ -1121,26 +1105,20 @@ vardef opt_lbls @# (text LBL) expr left_lbls=
     fi
     lbl_num:=lbl_num+1;
   endfor
+  string @#.l;
+  string @#.r;
   if lbl_num=0:
-    string @#.l;
-    string @#.r;
     @#.l:="";
     @#.r:="";
   elseif lbl_num=1:
     if left_lbls:
-      scantokens (arg_type fst_lbl) @#.l;
-      string @#.r;
       @#.l:=fst_lbl;
       @#.r:="";
     else:
-      string @#.l;
-      scantokens (arg_type fst_lbl) @#.r;
       @#.l:="";
       @#.r:=fst_lbl;
     fi
   else:
-    scantokens (arg_type fst_lbl) @#.l;
-    scantokens (arg_type snd_lbl) @#.r;
     @#.l:=fst_lbl;
     @#.r:=snd_lbl;
   fi
@@ -1339,8 +1317,8 @@ enddef;
 % 1. Global parameters
 %
 
-string drv_l_dlm; % left delimiter LaTeX code
-string drv_r_dlm; % right delimiter LaTeX code
+string drv_ldlm_str; % left delimiter LaTeX code
+string drv_rdlm_str; % right delimiter LaTeX code
 
 %
 % 2. Macros
@@ -1352,16 +1330,16 @@ vardef minmax_y[]=(
       ypart jdg[@].c-num_hg+iln_hg[(iln_sty[ccl[@]])]
         +min_clr_scl*min_clr[drv_sty]/2
     else:
-      smin_y[@]-min_clr_scl*min_clr[drv_sty]
+      sub_min_y[@]-min_clr_scl*min_clr[drv_sty]
     fi,
-    smax_y[@]+min_clr_scl*min_clr[drv_sty]
+    sub_max_y[@]+min_clr_scl*min_clr[drv_sty]
   else:
-    smin_y[@]-min_clr_scl*min_clr[drv_sty],
+    sub_min_y[@]-min_clr_scl*min_clr[drv_sty],
     if known ccl[@]:
-      ypart jdg[@].c-den_dp-iln_hg[(iln_sty[ccl[@]])]
+      ypart jdg[@].c-den_dp+iln_dp[(iln_sty[ccl[@]])]
         -min_clr_scl*min_clr[drv_sty]/2
     else:
-      smax_y[@]+min_clr_scl*min_clr[drv_sty]
+      sub_max_y[@]+min_clr_scl*min_clr[drv_sty]
     fi
   fi)
 enddef;
@@ -1374,9 +1352,9 @@ vardef delim @# expr dlm_len=
   rule_str:="\rule{0bp}{"&(decimal(dlm_len/2+axis_hg[drv_sty]))&"bp}";
   dlm_str:=
     if str @#="l":
-      "\left"&drv_l_dlm&rule_str&"\right."
+      "\left"&drv_ldlm_str&rule_str&"\right."
     else:
-      "\left."&rule_str&"\right"&drv_r_dlm
+      "\left."&rule_str&"\right"&drv_rdlm_str
     fi;
   dlm_pct:=mth_tex[drv_sty] dlm_str;
   dlm_dp:=depth dlm_pct;
@@ -1472,7 +1450,7 @@ vardef drv_check_root[]=
       fi
     fi
     if unknown boxed[@]:
-      boxed[@]:=false;
+      boxed[@]:=drv_boxmode_on;
     fi
   fi
 enddef;
@@ -1490,8 +1468,8 @@ vardef drv_check=
       save root_str;
       string root_str;
       root_str:=decimal root_idx;
-      for idx=1 upto root_num-1:
-        root_idx:=root[idx];
+      for root_rnk=1 upto root_num-1:
+        root_idx:=root[root_rnk];
         drv_check_root[root_idx];
         root_str:=root_str&", "&(decimal root_idx);
       endfor
@@ -1507,70 +1485,96 @@ enddef;
 
 vardef drv_build_root[]=
   %
+  % orientation
+  %
+  if drv_bot_roots:
+    ypart iln[@].c=ypart jdg[@].c-den_dp;
+    sub_min_y[@]:=ypart jdg[@].c+jdg[@].dp;
+    sub_max_y[@]:=
+      if iln_sty[@]=0:
+        ypart jdg[@].c+jdg[@].hg
+      else:
+        ypart iln[@].c+iln_hg[iln_sty[@]]
+      fi;
+    for prm_rnk=0 upto prm_num[@]-1:
+      ypart jdg[prm[@][prm_rnk]].c=ypart iln[@].c+num_hg;
+      drv_build_root[prm[@][prm_rnk]];
+      sub_max_y[@]:=max(sub_max_y[@], sub_max_y[prm[@][prm_rnk]]);
+    endfor
+  else:
+    ypart iln[@].c=ypart jdg[@].c-num_hg;
+    sub_min_y[@]:=
+      if iln_sty[@]=0:
+        ypart jdg[@].c+jdg[@].dp
+      else:
+        ypart iln[@].c+iln_dp[iln_sty[@]]
+      fi;
+    sub_max_y[@]:=ypart jdg[@].c+jdg[@].hg;
+    for prm_rnk=0 upto prm_num[@]-1:
+      ypart jdg[prm[@][prm_rnk]].c=ypart iln[@].c+den_dp;
+      drv_build_root[prm[@][prm_rnk]];
+      sub_min_y[@]:=min(sub_min_y[@], sub_min_y[prm[@][prm_rnk]]);
+    endfor
+  fi
+  %
   % premises junction (from left to right)
   %
-  for prm_rnk=0 upto  prm_num[@]-1:
-    drv_build_root[prm[@][prm_rnk]];
-    if prm_rnk>0:
-      save ll_idx, lr_idx, rl_idx, rr_idx;
-      save lmax_x, rmin_x, min_skp;
-      numeric ll_idx, lr_idx, rl_idx, rr_idx;
-      numeric lmax_x, rmin_x, min_skp;
-      ypart jdg[prm[@][prm_rnk-1]].c=ypart jdg[prm[@][prm_rnk]].c;
-      ll_idx:=prm[@][0];
-      lr_idx:=prm[@][prm_rnk-1];
-      rl_idx:=prm[@][prm_rnk];
-      rr_idx:=prm[@][prm_rnk];
-      lmax_x:=imax_x[lr_idx];
-      rmin_x:=imin_x[rl_idx];
-      min_skp[0]:=rmin_x-lmax_x;
-      forever:
-        exitif (unknown r_prm[lr_idx]) or (unknown l_prm[rl_idx]);
-        ll_idx:=l_prm[ll_idx];
-        lr_idx:=r_prm[lr_idx];
-        rl_idx:=l_prm[rl_idx];
-        rr_idx:=r_prm[rr_idx];
-        lmax_x:=max(lmax_x, imax_x[lr_idx]);
-        rmin_x:=min(rmin_x, imin_x[rl_idx]);
-        min_skp[0]:=min(min_skp[0], imin_x[rl_idx]-imax_x[lr_idx]);
-      endfor
-      min_skp[1]:=rmin_x-lmax_x;
-      if known r_prm[lr_idx]:
-        r_prm[rr_idx]:= r_prm[lr_idx];
-        lmax_x:=smax_x[lr_idx];
-      elseif known l_prm[rl_idx]:
-        l_prm[ll_idx]:=l_prm[rl_idx];
-        rmin_x:=smin_x[rl_idx];
-      fi
-      min_skp[2]:=rmin_x-lmax_x;
-      if jct_sty[@]<3:
-        min_skp[jct_sty[@]]=prm_skp_scl*prm_skp[drv_sty];
-      fi
+  for prm_rnk=1 upto  prm_num[@]-1:
+    save l_lmost, l_rmost, r_lmost, r_rmost;
+    save l_max_x, r_min_x, min_skp;
+    numeric l_lmost, l_rmost, r_lmost, r_rmost;
+    numeric l_max_x, r_min_x, min_skp[];
+    l_lmost:=prm[@][0];
+    l_rmost:=prm[@][prm_rnk-1];
+    r_lmost:=prm[@][prm_rnk];
+    r_rmost:=prm[@][prm_rnk];
+    l_max_x:=nfr_max_x[l_rmost];
+    r_min_x:=nfr_min_x[r_lmost];
+    min_skp[0]:=r_min_x-l_max_x;
+    forever:
+      exitif (unknown r_prm[l_rmost]) or (unknown l_prm[r_lmost]);
+      l_lmost:=l_prm[l_lmost];
+      l_rmost:=r_prm[l_rmost];
+      r_lmost:=l_prm[r_lmost];
+      r_rmost:=r_prm[r_rmost];
+      l_max_x:=max(l_max_x, nfr_max_x[l_rmost]);
+      r_min_x:=min(r_min_x, nfr_min_x[r_lmost]);
+      min_skp[0]:=min(min_skp[0], nfr_min_x[r_lmost]-nfr_max_x[l_rmost]);
+    endfor
+    min_skp[1]:=r_min_x-l_max_x;
+    if known r_prm[l_rmost]:
+      r_prm[r_rmost]:= r_prm[l_rmost];
+      l_max_x:=sub_max_x[l_rmost];
+    elseif known l_prm[r_lmost]:
+      l_prm[l_lmost]:=l_prm[r_lmost];
+      r_min_x:=sub_min_x[r_lmost];
+    fi
+    min_skp[2]:=r_min_x-l_max_x;
+    if jct_sty[@]<3:
+      min_skp[jct_sty[@]]=prm_skp_scl*prm_skp[drv_sty];
     fi
   endfor
-  if  prm_num[@]>0:
-    l_prm[@]:=prm[@][0];
-    r_prm[@]:=prm[@][prm_num[@]-1];
-  fi
   %
   % judgment alignment
   %
   if prm_num[@]=0:
-    imin_x[@]:=xpart jdg[@].l-jdg_skp_scl*jdg_skp[jdg_sty[drv_sty]];
-    imax_x[@]:=xpart jdg[@].r+jdg_skp_scl*jdg_skp[jdg_sty[drv_sty]];
+    nfr_min_x[@]:=xpart jdg[@].l;
+    nfr_max_x[@]:=xpart jdg[@].r;
   else:
+    l_prm[@]:=prm[@][0];
+    r_prm[@]:=prm[@][prm_num[@]-1];
     save l_xref, r_xref;
     l_xref=
-      if boxed[prm[@][0]]:
-        smin_x[prm[@][0]]
+      if boxed[l_prm[@]]:
+        sub_min_x[l_prm[@]]
       else:
-        xpart jdg[prm[@][0]].l
+        xpart jdg[l_prm[@]].l
       fi;
     r_xref=
-      if boxed[prm[@][prm_num[@]-1]]:
-        smax_x[prm[@][prm_num[@]-1]]
+      if boxed[r_prm[@]]:
+        sub_max_x[r_prm[@]]
       else:
-        xpart jdg[prm[@][prm_num[@]-1]].r
+        xpart jdg[r_prm[@]].r
       fi;
     if alg_sty[@]="l":
       xpart jdg[@].l=l_xref;
@@ -1579,10 +1583,8 @@ vardef drv_build_root[]=
     elseif alg_sty[@]="r":
       xpart jdg[@].r=r_xref;
     fi
-    imin_x[@]:=min(xpart jdg[@].l, l_xref)
-          -jdg_skp_scl*jdg_skp[jdg_sty[drv_sty]];
-    imax_x[@]:=max(xpart jdg[@].r, r_xref)
-          +jdg_skp_scl*jdg_skp[jdg_sty[drv_sty]];
+    nfr_min_x[@]:=min(xpart jdg[@].l, l_xref);
+    nfr_max_x[@]:=max(xpart jdg[@].r, r_xref);
   fi
   %
   % inference line
@@ -1590,7 +1592,7 @@ vardef drv_build_root[]=
   save iln_wd, iln_pct;
   numeric iln_wd;
   picture iln_pct;
-  iln_wd:=imax_x[@]-imin_x[@];
+  iln_wd:=nfr_max_x[@]-nfr_min_x[@]+2*jdg_skp_scl*jdg_skp[jdg_sty[drv_sty]];
   iln_pct:=((0, 0)--(iln_wd, 0)) drv_styled iln_sty[@];
   setbounds iln_pct to
     (0, ypart llcorner iln_pct)
@@ -1599,65 +1601,33 @@ vardef drv_build_root[]=
   --(iln_wd, ypart llcorner iln_pct)
   --cycle; % ! `linecap:=butt' and `linecap:=squared' -> same bounding box !
   box_init iln[@] (iln_pct);
-  xpart iln[@].c=(imin_x[@]+imax_x[@])/2;
-  %
-  % orientation, smin_y & smax_y
-  %
-  if drv_bot_roots:
-    ypart iln[@].c=ypart jdg[@].c-den_dp;
-    smin_y[@]:=ypart jdg[@].c+jdg[@].dp;
-    smax_y[@]:=
-      if iln_sty[@]=0:
-        ypart jdg[@].c+jdg[@].hg
-      else:
-        ypart iln[@].c+iln[@].hg
-      fi;
-    if prm_num[@]>0:
-      ypart iln[@].c=ypart jdg[prm[@][0]].c-num_hg;
-      for prm_rnk=0 upto prm_num[@]-1:
-        smax_y[@]:=max(smax_y[@], smax_y[prm[@][prm_rnk]]);
-      endfor;
-    fi
-  else:
-    ypart iln[@].c=ypart jdg[@].c-num_hg;
-    smin_y[@]:=
-      if iln_sty[@]=0:
-        ypart jdg[@].c+jdg[@].dp
-      else:
-        ypart iln[@].c+iln[@].dp
-      fi;
-    smax_y[@]:=ypart jdg[@].c+jdg[@].hg;
-    if prm_num[@]>0:
-      ypart iln[@].c=ypart jdg[prm[@][0]].c-den_dp;
-      for prm_rnk=0 upto prm_num[@]-1:
-        smin_y[@]:=min(smin_y[@], smin_y[prm[@][prm_rnk]]);
-      endfor;
-    fi
+  xpart iln[@].c=(nfr_min_x[@]+nfr_max_x[@])/2;
+  if iln_sty[@]>0:
+    nfr_min_x[@]:=xpart iln[@].l;
+    nfr_max_x[@]:=xpart iln[@].r;
   fi
   %
   % inference labels
   %
   if known l_ilb[@]:
     l_ilb[@].r=iln[@].l shifted (-ilb_skp_scl*ilb_skp[drv_sty], 0);
-    imin_x[@]:=xpart l_ilb[@].l;
-    smin_y[@]:=min(smin_y[@], ypart l_ilb[@].c+l_ilb[@].dp);
-    smax_y[@]:=max(smax_y[@], ypart l_ilb[@].c+l_ilb[@].hg);
+    nfr_min_x[@]:=xpart l_ilb[@].l;
+    sub_min_y[@]:=min(sub_min_y[@], ypart l_ilb[@].c+l_ilb[@].dp);
+    sub_max_y[@]:=max(sub_max_y[@], ypart l_ilb[@].c+l_ilb[@].hg);
   fi
   if known r_ilb[@]:
     r_ilb[@].l=iln[@].r shifted (ilb_skp_scl*ilb_skp[drv_sty], 0);
-    imax_x[@]:=xpart r_ilb[@].r;
-    smin_y[@]:=min(smin_y[@], ypart r_ilb[@].c+r_ilb[@].dp);
-    smax_y[@]:=max(smax_y[@], ypart r_ilb[@].c+r_ilb[@].hg);
+    nfr_max_x[@]:=xpart r_ilb[@].r;
+    sub_min_y[@]:=min(sub_min_y[@], ypart r_ilb[@].c+r_ilb[@].dp);
+    sub_max_y[@]:=max(sub_max_y[@], ypart r_ilb[@].c+r_ilb[@].hg);
   fi
   %
   % phantom steps
   %
   if known tgt[@]:
-    save phm_pth, phm_pct;
-    path phm_pth;
+    save bot_y, top_y, phm_pct;
+    numeric bot_y, top_y;
     picture phm_pct;
-    save top_y, mid_y, bot_y;
-    numeric top_y, bot_y;
     if drv_bot_roots:
       bot_y:=xpart minmax_y[@]+min_clr_scl*min_clr[drv_sty]/2;
       top_y:=xpart minmax_y[tgt[@]];
@@ -1665,85 +1635,78 @@ vardef drv_build_root[]=
       bot_y:=ypart minmax_y[tgt[@]];
       top_y:=ypart minmax_y[@]-min_clr_scl*min_clr[drv_sty]/2;
     fi
-    mid_y:=(top_y+bot_y)/2;
-    phm_pth:=(0, (bot_y-top_y)/2)--(0, (top_y-bot_y)/2);
-    phm_pct:=phm_pth drv_styled phm_sty[@];
+    phm_pct:=((0, (bot_y-top_y)/2)--(0, (top_y-bot_y)/2))
+      drv_styled phm_sty[@];
     box_init phm[@] (phm_pct shifted ((width phm_pct)/2, 0));
-    phm[@].c=(xpart jdg[@].c, mid_y);
-    imin_x[@]:=min(imin_x[@], xpart phm[@].l);
-    imax_x[@]:=max(imax_x[@], xpart phm[@].r);
+    phm[@].c=(xpart jdg[@].c, (top_y+bot_y)/2);
+    nfr_min_x[@]:=min(nfr_min_x[@], xpart phm[@].l);
+    nfr_max_x[@]:=max(nfr_max_x[@], xpart phm[@].r);
     %
     % phantom steps labels
     %
     if known l_plb[@]:
       l_plb[@].r=phm[@].l shifted (-plb_skp[drv_sty], 0);
-      imin_x[@]:=min(imin_x[@], xpart l_plb[@].l);
+      nfr_min_x[@]:=min(nfr_min_x[@], xpart l_plb[@].l);
     fi
     if known r_plb[@]:
       r_plb[@].l=phm[@].r shifted ( plb_skp[drv_sty], 0);
-      imax_x[@]:=max(imax_x[@], xpart r_plb[@].r);
+      nfr_max_x[@]:=max(nfr_max_x[@], xpart r_plb[@].r);
     fi
   fi
   %
-  % smin_x & smax_x
+  % sub_min_x & sub_max_x
   %
-  smin_x[@]:=imin_x[@];
-  smax_x[@]:=imax_x[@];
+  sub_min_x[@]:=nfr_min_x[@];
+  sub_max_x[@]:=nfr_max_x[@];
   for prm_rnk=0 upto prm_num[@]-1:
-    smin_x[@]:=min(smin_x[@], smin_x[prm[@][prm_rnk]]);
-    smax_x[@]:=max(smax_x[@], smax_x[prm[@][prm_rnk]]);
+    sub_min_x[@]:=min(sub_min_x[@], sub_min_x[prm[@][prm_rnk]]);
+    sub_max_x[@]:=max(sub_max_x[@], sub_max_x[prm[@][prm_rnk]]);
   endfor
   %
   % delimiters
   %
   if known l_dlb[@] or known r_dlb[@]:
-    save idx, mmy, min_y, max_y;
-    numeric idx, min_y, max_y;
+    save mmy, min_y, max_y;
+    numeric min_y, max_y;
     pair mmy;
     mmy:=minmax_y[@];
     min_y:=xpart mmy;
     max_y:=ypart mmy;
     if known l_dlb[@]:
       box_init l_dlm[@] (delim l (max_y-min_y));
-      l_dlm[@].r=(smin_x[@], (max_y+min_y)/2);
+      l_dlm[@].r=(sub_min_x[@], (max_y+min_y)/2);
       l_dlb[@].r=l_dlm[@].l;
-      smin_x[@]:=xpart l_dlb[@].l;
+      sub_min_x[@]:=xpart l_dlb[@].l;
     fi
     if known r_dlb[@]:
       box_init r_dlm[@] (delim r (max_y-min_y));
-      r_dlm[@].l=(smax_x[@], (max_y+min_y)/2);
+      r_dlm[@].l=(sub_max_x[@], (max_y+min_y)/2);
       r_dlb[@].l=r_dlm[@].r;
-      smax_x[@]:=xpart r_dlb[@].r;
+      sub_max_x[@]:=xpart r_dlb[@].r;
     fi
   fi
   if (known l_dlb[@]) or boxed[@]:
+    save idx;
+    numeric idx;
     idx:=@;
     forever:
-      imin_x[idx]:=smin_x[@];
+      nfr_min_x[idx]:=sub_min_x[@];
       exitif unknown l_prm[idx];
       idx:=l_prm[idx];
     endfor
   fi
   if (known r_dlb[@]) or boxed[@]:
+    save idx;
+    numeric idx;
     idx:=@;
     forever:
-      imax_x[idx]:=smax_x[@];
+      nfr_max_x[idx]:=sub_max_x[@];
       exitif unknown r_prm[idx];
       idx:=r_prm[idx];
     endfor
   fi
 enddef;
 
-vardef drv_build=
-  if not drv_checked:
-    drv_check;
-  fi
-  for idx=0 upto root_num-1:
-    drv_build_root[root[idx]];
-  endfor
-  drv_built:=true;
-enddef;
-
 %
 % Freezing
 %
@@ -1766,28 +1729,31 @@ vardef drv_freeze_root[]=
 enddef;
 
 vardef drv_freeze=
-  if not drv_built:
-    drv_build;
+  if not drv_checked:
+    drv_check;
   fi
   save root_idx;
   numeric root_idx;
-  root_idx:=root[0];
-  if unknown iln[root_idx].c:
-    %
-    % default math axis
-    %
-    if drv_axis_ref="iln":
-      iln[root_idx].c=(0, axis_hg[drv_sty]);
-    else: % drv_axis_ref="jdg"
-      jdg[root_idx].c=(0, axis_hg[drv_sty]);
+  for root_rnk=0 upto root_num-1:
+    root_idx:=root[root_rnk];
+    drv_build_root[root_idx];
+    if unknown xpart jdg[root_idx].c:
+      if root_rnk=0:
+        xpart jdg[root_idx].c=0;
+      else:
+        sub_min_x[root_idx]=sub_max_x[root[root_rnk-1]]
+          +prm_skp_scl*prm_skp[drv_sty];
+      fi
     fi
-    drv_freeze_root[root_idx];
-  fi
-  for idx=1 upto root_num-1:
-    root_idx:=root[idx];
-    if unknown iln[root_idx].c:
-      smin_x[root_idx]=smax_x[root[idx-1]]+prm_skp_scl*prm_skp[drv_sty];
-      ypart iln[root_idx].c=ypart iln[root[idx-1]].c;
+    if unknown ypart jdg[root_idx].c:
+      %
+      % default math axis
+      %
+      if drv_axis_ref="iln":
+        ypart iln[root_idx].c=axis_hg[drv_sty];
+      else: % drv_axis_ref="jdg"
+        ypart jdg[root_idx].c=axis_hg[drv_sty];
+      fi
     fi
     drv_freeze_root[root_idx];
   endfor
@@ -1892,12 +1858,12 @@ vardef drv_tree=
   if not drv_frozen:
     drv_freeze;
   fi
-  for root_idx=0 upto root_num-1:
+  for root_rnk=0 upto root_num-1:
     if drv_proofmode_on:
-      drv_tree_addto pct (root[root_idx]) withcolor prf_clr;
-      prf_tree_addto pct (root[root_idx]);
+      drv_tree_addto pct (root[root_rnk]) withcolor prf_clr;
+      prf_tree_addto pct (root[root_rnk]);
     else:
-      drv_tree_addto pct (root[root_idx]);
+      drv_tree_addto pct (root[root_rnk]);
     fi
   endfor
   pct
@@ -1914,13 +1880,13 @@ vardef drv_bbox[]=
     if known l_dlm[@].r:
       xpart l_dlm[@].r
     else:
-      smin_x[@]
+      sub_min_x[@]
     fi-jdg_skp_scl*jdg_skp[jdg_sty[drv_sty]];
   max_x:=
     if known r_dlm[@].l:
       xpart l_dlm[@].l
     else:
-      smax_x[@]
+      sub_max_x[@]
     fi+jdg_skp_scl*jdg_skp[jdg_sty[drv_sty]];
   mmy:=minmax_y[@];
   min_y:=xpart mmy;
@@ -2158,7 +2124,8 @@ vardef drv_axis_reference suffix ref_sfx=
   string ref_str;
   ref_str:=str ref_sfx;
   if (ref_str<>"iln") and (ref_str<>"jdg"):
-    drv_errhelp "Valid identifiers are iln (inference line axis) and"&
+    drv_errhelp "Valid identifiers are"&
+      " iln (inference line axis) and"&
       " jdg (judgment math-axis).";
     drv_errmessage (ref_str&" is not a valid reference identifier");
   else:
@@ -2168,9 +2135,9 @@ enddef;
 
 vardef drv_delimiter (suffix pos_sfx) (expr dlm_str)=
   if check_position_left (pos_sfx, true):
-    drv_l_dlm:=dlm_str;
+    drv_ldlm_str:=dlm_str;
   else:
-    drv_r_dlm:=dlm_str;
+    drv_rdlm_str:=dlm_str;
   fi
 enddef;
 
diff --git a/Master/texmf-dist/metapost/drv/drv.mp b/Master/texmf-dist/metapost/drv/drv.mp
index 5eb38396144..69f2f9f72c7 100644
--- a/Master/texmf-dist/metapost/drv/drv.mp
+++ b/Master/texmf-dist/metapost/drv/drv.mp
@@ -1,4 +1,4 @@
-%% drv.mp 0.93
+%% drv.mp 0.94
 %% Copyright 2009 Laurent M\'ehats
 %
 % This work may be distributed and/or modified under the
@@ -188,10 +188,10 @@
 %
 %   drv_left_delimiter <str>
 %	<str>		left delimiter math-mode LaTeX code
-%			  "("	$($
-%			  "["	$[$
-%			  "\lbrace"	$\lbrace$
-%			  "\langle"	$\langle$
+%			  "("
+%			  "["
+%			  "\lbrace"
+%			  "\langle"
 %			  etc.
 %
 %   drv_right_delimiter <str>
@@ -391,8 +391,8 @@ drv_message "done.";
 % writing LaTeX picture definitions
 %
 
-numeric tex_pct_idx;
-tex_pct_idx:=0;
+numeric tex_pct_rnk;
+tex_pct_rnk:=0;
 
 % Math style indices: 0, 1, 2, 3
 string mth_sty_str[];
@@ -410,14 +410,14 @@ vardef drv_tex[] expr tex_str=
   string def_str;
   picture pct;
   def_str:="btex{"&drv_fontsize&"$"&mth_sty_str[@]&"{}"&tex_str&"{}$}etex;";
-  write "tex_pct["&(decimal tex_pct_idx)&"]:="&def_str to delayed_tex_file;
+  write "tex_pct["&(decimal tex_pct_rnk)&"]:="&def_str to delayed_tex_file;
   pct:=
-    if known tex_pct[tex_pct_idx]:
-      tex_pct[tex_pct_idx]
+    if known tex_pct[tex_pct_rnk]:
+      tex_pct[tex_pct_rnk]
     else:
       nullpicture
     fi;
-  tex_pct_idx:=tex_pct_idx+1;
+  tex_pct_rnk:=tex_pct_rnk+1;
   pct
 enddef;
 
@@ -644,31 +644,31 @@ vardef drv_beginfig=
   numeric iln_sty[];
   numeric l_prm[], r_prm[];
   %
-  % imin_x[i]	inference minimal x
-  % l_dlb[i]	left delimiter label drv-box
-  % l_dlm[i]	left delimiter drv-box
-  % l_ilb[i]	left label drv-box
-  % iln[i]	inference line drv-box
-  % r_ilb[i]	right label drv-box
-  % r_dlm[i]	right delimiter drv-box
-  % r_dlb[i]	right delimiter label drv-box
-  % imax_x[i]	inference maximal x
+  % nfr_min_x[i]	inference minimal x
+  % l_dlb[i]		left delimiter label drv-box
+  % l_dlm[i]		left delimiter drv-box
+  % l_ilb[i]		left label drv-box
+  % iln[i]		inference line drv-box
+  % r_ilb[i]		right label drv-box
+  % r_dlm[i]		right delimiter drv-box
+  % r_dlb[i]		right delimiter label drv-box
+  % nfr_max_x[i]	inference maximal x
   %
-  numeric imin_x[];
+  numeric nfr_min_x[];
   drv_box "l_dlb[]", "l_dlm[]", "l_ilb[]";
   drv_box "iln[]";
   drv_box "r_ilb[]", "r_dlm[]", "r_dlb[]";
-  numeric imax_x[];
+  numeric nfr_max_x[];
   %
   % Sub-trees
   %
-  % smin_x[i]	sub-tree minimal x
-  % smax_x[i]	sub-tree maximal x
-  % smin_y[i]	sub-tree minimal y
-  % smax_y[i]	sub-tree maximal y
-  % boxed[i]	boolean
+  % sub_min_x[i]	sub-tree minimal x
+  % sub_max_x[i]	sub-tree maximal x
+  % sub_min_y[i]	sub-tree minimal y
+  % sub_max_y[i]	sub-tree maximal y
+  % boxed[i]		boolean
   %
-  numeric smin_x[], smax_x[], smin_y[], smax_y[];
+  numeric sub_min_x[], sub_max_x[], sub_min_y[], sub_max_y[];
   boolean boxed[];
   %
   % Pen initialization
@@ -694,14 +694,13 @@ vardef drv_beginfig=
   %
   % root_num	number of roots
   % root[i]	root index (i ranges from 0 to root_num-1)
-  % drv_built	boolean
+  % drv_checked	boolean
   % drv_frozen	boolean
   %
   numeric root_num, root[];
-  boolean drv_checked, drv_built, drv_frozen;
+  boolean drv_checked, drv_frozen;
   root_num:=0;
   drv_checked:=false;
-  drv_built:=false;
   drv_frozen:=false;
   %
   % Phantom steps
@@ -819,27 +818,19 @@ vardef jgm[] text SUB=
     jdg_wd:=0;
     sbj_rnk:=0;
     for sub=SUB:
-      sbj_pct:=
-        if picture sub:
-          sub
-        elseif sub<>"":
-          mth_tex[jdg_sty[drv_sty]] sub
-        else:
-          nullpicture
-        fi;
+      sbj_pct:=mth_tex[jdg_sty[drv_sty]] sub;
       box_init sbj[@][sbj_rnk] (sbj_pct);
-      if sbj_rnk>0:
-        sbj[@][sbj_rnk-1].r=sbj[@][sbj_rnk].l;
+      if sbj_rnk>0:				% non mandatory test
+        sbj[@][sbj_rnk-1].r=sbj[@][sbj_rnk].l;	% irrelevant if rnk=0
       fi
       addto jdg_pct also sbj_pct shifted (jdg_wd, 0);
-      jdg_wd:=width jdg_pct;
+      jdg_wd:=jdg_wd+width sbj_pct;
       sbj_rnk:=sbj_rnk+1;
     endfor
     sbj_num[@]:=sbj_rnk;
     box_init jdg[@] (jdg_pct);
-    if sbj_num[@]>0:
-      jdg[@].l=sbj[@][0].l;
-      jdg[@].r=sbj[@][sbj_num[@]-1].r;
+    if sbj_num[@]>0:				% non mandatory test
+      jdg[@].l=sbj[@][0].l;			% irrelevant if sbj_num=0
     fi
   fi
 enddef;
@@ -850,6 +841,19 @@ enddef;
 % Inference declarations
 %
 
+%
+% 1. Global parameters
+%
+
+numeric drv_jct_sty;	% default junction style
+string  drv_alg_sty;	% default junction style
+numeric drv_iln_sty;	% default inference line path-style
+numeric drv_phm_sty;	% default phantom steps path-style
+
+%
+% 2. Macros
+%
+
 vardef check_junction_style (suffix sty_sfx) (expr default)=
   save sty_str;
   string sty_str;
@@ -931,13 +935,9 @@ vardef check_path_style (suffix sty_sfx) (expr default)=
   fi
 enddef;
 
-vardef opt_init[] @# expr arg=
-  if picture arg:
-    if arg<>nullpicture:
-      box_init @# (arg);
-    fi
-  elseif arg<>"":
-    box_init @# (mth_tex[@] arg);
+vardef opt_init[] @# expr str=
+  if str<>"":
+    box_init @# (mth_tex[@] str);
   fi
 enddef;
 
@@ -971,17 +971,17 @@ vardef NFR[] (text PRM) (expr lilb, rilb, ldlb, rdlb)
           %
           % roots list update
           %
-          save root_idx;
-          numeric root_idx;
-          root_idx:=0;
+          save root_rnk;
+          numeric root_rnk;
+          root_rnk:=0;
           forever:
-            exitif root[root_idx]=prm_idx;
-            root_idx:=root_idx+1;
+            exitif root[root_rnk]=prm_idx;
+            root_rnk:=root_rnk+1;
           endfor
           forever:
-            exitif root_idx=root_num-1;
-            root[root_idx]:=root[root_idx+1];
-            root_idx:=root_idx+1;
+            exitif root_rnk=root_num-1;
+            root[root_rnk]:=root[root_rnk+1];
+            root_rnk:=root_rnk+1;
           endfor
           root_num:=root_num-1;
         fi
@@ -1033,9 +1033,6 @@ vardef NFR[] (text PRM) (expr lilb, rilb, ldlb, rdlb)
     jct_sty[@]:=check_junction_style (j_sty, drv_jct_sty);
     alg_sty[@]:=check_alignment_style (a_sty, drv_alg_sty);
     iln_sty[@]:=check_path_style (i_sty, drv_iln_sty);
-    if drv_boxmode_on:
-      boxed[@]:=true;
-    fi
   fi
 enddef;
 
@@ -1051,23 +1048,23 @@ vardef MVD[] (expr inf_num, lplb, rplb) (suffix a_sty, p_sty)=
     drv_errmessage (decimal inf_num)&" is not a valid number of inference"&
       " steps";
   else:
-    save aux_idx, aux_sty, phm_jdg;
-    numeric aux_idx, aux_sty;
+    save prm_idx, pth_sty, phm_jdg;
+    numeric prm_idx, pth_sty;
     picture phm_jdg;
-    aux_sty:=check_path_style (p_sty, drv_phm_sty);
+    pth_sty:=check_path_style (p_sty, drv_phm_sty);
     phm_jdg:=nullpicture;
-    setbounds phm_jdg to (0, 0)--(iln_hg[aux_sty]-iln_dp[aux_sty], 0)--cycle;
-    aux_idx:=@;
+    setbounds phm_jdg to (0, 0)--(iln_hg[pth_sty]-iln_dp[pth_sty], 0)--cycle;
+    prm_idx:=@;
     for i=1 upto inf_num:
       phm_idx:=phm_idx-1;
       box_init jdg[phm_idx] (phm_jdg);
       sbj_num[phm_idx]:=0;
-      NFR[phm_idx] (aux_idx) ("", "", "", "", 0, a_sty, 0);
-      aux_idx:=phm_idx;
+      NFR[phm_idx] (prm_idx) ("", "", "", "", 0, a_sty, 0);
+      prm_idx:=phm_idx;
     endfor
     src[@]:=phm_idx;
     tgt[phm_idx]:=@;
-    phm_sty[phm_idx]:=aux_sty;
+    phm_sty[phm_idx]:=pth_sty;
     %
     % lplb, rplb: phantom steps labels
     %
@@ -1086,33 +1083,20 @@ enddef;
 % Optional labels & shorthands
 %
 
-numeric drv_jct_sty;	% default junction style
-string  drv_alg_sty;	% default junction style
-numeric drv_iln_sty;	% default inference line path-style
-numeric drv_phm_sty;	% default phantom steps path-style
-
 boolean drv_left_ilb;	% inference labels on the left
 boolean drv_left_dlb;	% delimiter labels (hence delimiters) on the left
 boolean drv_left_plb;	% phantom steps labels on the left
 
-vardef arg_type expr arg=
-  if picture arg:
-    "picture"
-  else:
-    "string"
-  fi
-enddef;
-
 vardef opt_lbls @# (text LBL) expr left_lbls=
   save lbl_num, fst_lbl, snd_lbl;
   numeric lbl_num;
   lbl_num:=0;
   for lbl=LBL:
     if lbl_num=0:
-      scantokens (arg_type lbl) fst_lbl;
+      string fst_lbl;
       fst_lbl:=lbl;
     elseif lbl_num=1:
-      scantokens (arg_type lbl) snd_lbl;
+      string snd_lbl;
       snd_lbl:=lbl;
     else:
       drv_errhelp "At most two labels can be specified:"&
@@ -1121,26 +1105,20 @@ vardef opt_lbls @# (text LBL) expr left_lbls=
     fi
     lbl_num:=lbl_num+1;
   endfor
+  string @#.l;
+  string @#.r;
   if lbl_num=0:
-    string @#.l;
-    string @#.r;
     @#.l:="";
     @#.r:="";
   elseif lbl_num=1:
     if left_lbls:
-      scantokens (arg_type fst_lbl) @#.l;
-      string @#.r;
       @#.l:=fst_lbl;
       @#.r:="";
     else:
-      string @#.l;
-      scantokens (arg_type fst_lbl) @#.r;
       @#.l:="";
       @#.r:=fst_lbl;
     fi
   else:
-    scantokens (arg_type fst_lbl) @#.l;
-    scantokens (arg_type snd_lbl) @#.r;
     @#.l:=fst_lbl;
     @#.r:=snd_lbl;
   fi
@@ -1339,8 +1317,8 @@ enddef;
 % 1. Global parameters
 %
 
-string drv_l_dlm; % left delimiter LaTeX code
-string drv_r_dlm; % right delimiter LaTeX code
+string drv_ldlm_str; % left delimiter LaTeX code
+string drv_rdlm_str; % right delimiter LaTeX code
 
 %
 % 2. Macros
@@ -1352,16 +1330,16 @@ vardef minmax_y[]=(
       ypart jdg[@].c-num_hg+iln_hg[(iln_sty[ccl[@]])]
         +min_clr_scl*min_clr[drv_sty]/2
     else:
-      smin_y[@]-min_clr_scl*min_clr[drv_sty]
+      sub_min_y[@]-min_clr_scl*min_clr[drv_sty]
     fi,
-    smax_y[@]+min_clr_scl*min_clr[drv_sty]
+    sub_max_y[@]+min_clr_scl*min_clr[drv_sty]
   else:
-    smin_y[@]-min_clr_scl*min_clr[drv_sty],
+    sub_min_y[@]-min_clr_scl*min_clr[drv_sty],
     if known ccl[@]:
-      ypart jdg[@].c-den_dp-iln_hg[(iln_sty[ccl[@]])]
+      ypart jdg[@].c-den_dp+iln_dp[(iln_sty[ccl[@]])]
         -min_clr_scl*min_clr[drv_sty]/2
     else:
-      smax_y[@]+min_clr_scl*min_clr[drv_sty]
+      sub_max_y[@]+min_clr_scl*min_clr[drv_sty]
     fi
   fi)
 enddef;
@@ -1374,9 +1352,9 @@ vardef delim @# expr dlm_len=
   rule_str:="\rule{0bp}{"&(decimal(dlm_len/2+axis_hg[drv_sty]))&"bp}";
   dlm_str:=
     if str @#="l":
-      "\left"&drv_l_dlm&rule_str&"\right."
+      "\left"&drv_ldlm_str&rule_str&"\right."
     else:
-      "\left."&rule_str&"\right"&drv_r_dlm
+      "\left."&rule_str&"\right"&drv_rdlm_str
     fi;
   dlm_pct:=mth_tex[drv_sty] dlm_str;
   dlm_dp:=depth dlm_pct;
@@ -1472,7 +1450,7 @@ vardef drv_check_root[]=
       fi
     fi
     if unknown boxed[@]:
-      boxed[@]:=false;
+      boxed[@]:=drv_boxmode_on;
     fi
   fi
 enddef;
@@ -1490,8 +1468,8 @@ vardef drv_check=
       save root_str;
       string root_str;
       root_str:=decimal root_idx;
-      for idx=1 upto root_num-1:
-        root_idx:=root[idx];
+      for root_rnk=1 upto root_num-1:
+        root_idx:=root[root_rnk];
         drv_check_root[root_idx];
         root_str:=root_str&", "&(decimal root_idx);
       endfor
@@ -1507,70 +1485,96 @@ enddef;
 
 vardef drv_build_root[]=
   %
+  % orientation
+  %
+  if drv_bot_roots:
+    ypart iln[@].c=ypart jdg[@].c-den_dp;
+    sub_min_y[@]:=ypart jdg[@].c+jdg[@].dp;
+    sub_max_y[@]:=
+      if iln_sty[@]=0:
+        ypart jdg[@].c+jdg[@].hg
+      else:
+        ypart iln[@].c+iln_hg[iln_sty[@]]
+      fi;
+    for prm_rnk=0 upto prm_num[@]-1:
+      ypart jdg[prm[@][prm_rnk]].c=ypart iln[@].c+num_hg;
+      drv_build_root[prm[@][prm_rnk]];
+      sub_max_y[@]:=max(sub_max_y[@], sub_max_y[prm[@][prm_rnk]]);
+    endfor
+  else:
+    ypart iln[@].c=ypart jdg[@].c-num_hg;
+    sub_min_y[@]:=
+      if iln_sty[@]=0:
+        ypart jdg[@].c+jdg[@].dp
+      else:
+        ypart iln[@].c+iln_dp[iln_sty[@]]
+      fi;
+    sub_max_y[@]:=ypart jdg[@].c+jdg[@].hg;
+    for prm_rnk=0 upto prm_num[@]-1:
+      ypart jdg[prm[@][prm_rnk]].c=ypart iln[@].c+den_dp;
+      drv_build_root[prm[@][prm_rnk]];
+      sub_min_y[@]:=min(sub_min_y[@], sub_min_y[prm[@][prm_rnk]]);
+    endfor
+  fi
+  %
   % premises junction (from left to right)
   %
-  for prm_rnk=0 upto  prm_num[@]-1:
-    drv_build_root[prm[@][prm_rnk]];
-    if prm_rnk>0:
-      save ll_idx, lr_idx, rl_idx, rr_idx;
-      save lmax_x, rmin_x, min_skp;
-      numeric ll_idx, lr_idx, rl_idx, rr_idx;
-      numeric lmax_x, rmin_x, min_skp;
-      ypart jdg[prm[@][prm_rnk-1]].c=ypart jdg[prm[@][prm_rnk]].c;
-      ll_idx:=prm[@][0];
-      lr_idx:=prm[@][prm_rnk-1];
-      rl_idx:=prm[@][prm_rnk];
-      rr_idx:=prm[@][prm_rnk];
-      lmax_x:=imax_x[lr_idx];
-      rmin_x:=imin_x[rl_idx];
-      min_skp[0]:=rmin_x-lmax_x;
-      forever:
-        exitif (unknown r_prm[lr_idx]) or (unknown l_prm[rl_idx]);
-        ll_idx:=l_prm[ll_idx];
-        lr_idx:=r_prm[lr_idx];
-        rl_idx:=l_prm[rl_idx];
-        rr_idx:=r_prm[rr_idx];
-        lmax_x:=max(lmax_x, imax_x[lr_idx]);
-        rmin_x:=min(rmin_x, imin_x[rl_idx]);
-        min_skp[0]:=min(min_skp[0], imin_x[rl_idx]-imax_x[lr_idx]);
-      endfor
-      min_skp[1]:=rmin_x-lmax_x;
-      if known r_prm[lr_idx]:
-        r_prm[rr_idx]:= r_prm[lr_idx];
-        lmax_x:=smax_x[lr_idx];
-      elseif known l_prm[rl_idx]:
-        l_prm[ll_idx]:=l_prm[rl_idx];
-        rmin_x:=smin_x[rl_idx];
-      fi
-      min_skp[2]:=rmin_x-lmax_x;
-      if jct_sty[@]<3:
-        min_skp[jct_sty[@]]=prm_skp_scl*prm_skp[drv_sty];
-      fi
+  for prm_rnk=1 upto  prm_num[@]-1:
+    save l_lmost, l_rmost, r_lmost, r_rmost;
+    save l_max_x, r_min_x, min_skp;
+    numeric l_lmost, l_rmost, r_lmost, r_rmost;
+    numeric l_max_x, r_min_x, min_skp[];
+    l_lmost:=prm[@][0];
+    l_rmost:=prm[@][prm_rnk-1];
+    r_lmost:=prm[@][prm_rnk];
+    r_rmost:=prm[@][prm_rnk];
+    l_max_x:=nfr_max_x[l_rmost];
+    r_min_x:=nfr_min_x[r_lmost];
+    min_skp[0]:=r_min_x-l_max_x;
+    forever:
+      exitif (unknown r_prm[l_rmost]) or (unknown l_prm[r_lmost]);
+      l_lmost:=l_prm[l_lmost];
+      l_rmost:=r_prm[l_rmost];
+      r_lmost:=l_prm[r_lmost];
+      r_rmost:=r_prm[r_rmost];
+      l_max_x:=max(l_max_x, nfr_max_x[l_rmost]);
+      r_min_x:=min(r_min_x, nfr_min_x[r_lmost]);
+      min_skp[0]:=min(min_skp[0], nfr_min_x[r_lmost]-nfr_max_x[l_rmost]);
+    endfor
+    min_skp[1]:=r_min_x-l_max_x;
+    if known r_prm[l_rmost]:
+      r_prm[r_rmost]:= r_prm[l_rmost];
+      l_max_x:=sub_max_x[l_rmost];
+    elseif known l_prm[r_lmost]:
+      l_prm[l_lmost]:=l_prm[r_lmost];
+      r_min_x:=sub_min_x[r_lmost];
+    fi
+    min_skp[2]:=r_min_x-l_max_x;
+    if jct_sty[@]<3:
+      min_skp[jct_sty[@]]=prm_skp_scl*prm_skp[drv_sty];
     fi
   endfor
-  if  prm_num[@]>0:
-    l_prm[@]:=prm[@][0];
-    r_prm[@]:=prm[@][prm_num[@]-1];
-  fi
   %
   % judgment alignment
   %
   if prm_num[@]=0:
-    imin_x[@]:=xpart jdg[@].l-jdg_skp_scl*jdg_skp[jdg_sty[drv_sty]];
-    imax_x[@]:=xpart jdg[@].r+jdg_skp_scl*jdg_skp[jdg_sty[drv_sty]];
+    nfr_min_x[@]:=xpart jdg[@].l;
+    nfr_max_x[@]:=xpart jdg[@].r;
   else:
+    l_prm[@]:=prm[@][0];
+    r_prm[@]:=prm[@][prm_num[@]-1];
     save l_xref, r_xref;
     l_xref=
-      if boxed[prm[@][0]]:
-        smin_x[prm[@][0]]
+      if boxed[l_prm[@]]:
+        sub_min_x[l_prm[@]]
       else:
-        xpart jdg[prm[@][0]].l
+        xpart jdg[l_prm[@]].l
       fi;
     r_xref=
-      if boxed[prm[@][prm_num[@]-1]]:
-        smax_x[prm[@][prm_num[@]-1]]
+      if boxed[r_prm[@]]:
+        sub_max_x[r_prm[@]]
       else:
-        xpart jdg[prm[@][prm_num[@]-1]].r
+        xpart jdg[r_prm[@]].r
       fi;
     if alg_sty[@]="l":
       xpart jdg[@].l=l_xref;
@@ -1579,10 +1583,8 @@ vardef drv_build_root[]=
     elseif alg_sty[@]="r":
       xpart jdg[@].r=r_xref;
     fi
-    imin_x[@]:=min(xpart jdg[@].l, l_xref)
-          -jdg_skp_scl*jdg_skp[jdg_sty[drv_sty]];
-    imax_x[@]:=max(xpart jdg[@].r, r_xref)
-          +jdg_skp_scl*jdg_skp[jdg_sty[drv_sty]];
+    nfr_min_x[@]:=min(xpart jdg[@].l, l_xref);
+    nfr_max_x[@]:=max(xpart jdg[@].r, r_xref);
   fi
   %
   % inference line
@@ -1590,7 +1592,7 @@ vardef drv_build_root[]=
   save iln_wd, iln_pct;
   numeric iln_wd;
   picture iln_pct;
-  iln_wd:=imax_x[@]-imin_x[@];
+  iln_wd:=nfr_max_x[@]-nfr_min_x[@]+2*jdg_skp_scl*jdg_skp[jdg_sty[drv_sty]];
   iln_pct:=((0, 0)--(iln_wd, 0)) drv_styled iln_sty[@];
   setbounds iln_pct to
     (0, ypart llcorner iln_pct)
@@ -1599,65 +1601,33 @@ vardef drv_build_root[]=
   --(iln_wd, ypart llcorner iln_pct)
   --cycle; % ! `linecap:=butt' and `linecap:=squared' -> same bounding box !
   box_init iln[@] (iln_pct);
-  xpart iln[@].c=(imin_x[@]+imax_x[@])/2;
-  %
-  % orientation, smin_y & smax_y
-  %
-  if drv_bot_roots:
-    ypart iln[@].c=ypart jdg[@].c-den_dp;
-    smin_y[@]:=ypart jdg[@].c+jdg[@].dp;
-    smax_y[@]:=
-      if iln_sty[@]=0:
-        ypart jdg[@].c+jdg[@].hg
-      else:
-        ypart iln[@].c+iln[@].hg
-      fi;
-    if prm_num[@]>0:
-      ypart iln[@].c=ypart jdg[prm[@][0]].c-num_hg;
-      for prm_rnk=0 upto prm_num[@]-1:
-        smax_y[@]:=max(smax_y[@], smax_y[prm[@][prm_rnk]]);
-      endfor;
-    fi
-  else:
-    ypart iln[@].c=ypart jdg[@].c-num_hg;
-    smin_y[@]:=
-      if iln_sty[@]=0:
-        ypart jdg[@].c+jdg[@].dp
-      else:
-        ypart iln[@].c+iln[@].dp
-      fi;
-    smax_y[@]:=ypart jdg[@].c+jdg[@].hg;
-    if prm_num[@]>0:
-      ypart iln[@].c=ypart jdg[prm[@][0]].c-den_dp;
-      for prm_rnk=0 upto prm_num[@]-1:
-        smin_y[@]:=min(smin_y[@], smin_y[prm[@][prm_rnk]]);
-      endfor;
-    fi
+  xpart iln[@].c=(nfr_min_x[@]+nfr_max_x[@])/2;
+  if iln_sty[@]>0:
+    nfr_min_x[@]:=xpart iln[@].l;
+    nfr_max_x[@]:=xpart iln[@].r;
   fi
   %
   % inference labels
   %
   if known l_ilb[@]:
     l_ilb[@].r=iln[@].l shifted (-ilb_skp_scl*ilb_skp[drv_sty], 0);
-    imin_x[@]:=xpart l_ilb[@].l;
-    smin_y[@]:=min(smin_y[@], ypart l_ilb[@].c+l_ilb[@].dp);
-    smax_y[@]:=max(smax_y[@], ypart l_ilb[@].c+l_ilb[@].hg);
+    nfr_min_x[@]:=xpart l_ilb[@].l;
+    sub_min_y[@]:=min(sub_min_y[@], ypart l_ilb[@].c+l_ilb[@].dp);
+    sub_max_y[@]:=max(sub_max_y[@], ypart l_ilb[@].c+l_ilb[@].hg);
   fi
   if known r_ilb[@]:
     r_ilb[@].l=iln[@].r shifted (ilb_skp_scl*ilb_skp[drv_sty], 0);
-    imax_x[@]:=xpart r_ilb[@].r;
-    smin_y[@]:=min(smin_y[@], ypart r_ilb[@].c+r_ilb[@].dp);
-    smax_y[@]:=max(smax_y[@], ypart r_ilb[@].c+r_ilb[@].hg);
+    nfr_max_x[@]:=xpart r_ilb[@].r;
+    sub_min_y[@]:=min(sub_min_y[@], ypart r_ilb[@].c+r_ilb[@].dp);
+    sub_max_y[@]:=max(sub_max_y[@], ypart r_ilb[@].c+r_ilb[@].hg);
   fi
   %
   % phantom steps
   %
   if known tgt[@]:
-    save phm_pth, phm_pct;
-    path phm_pth;
+    save bot_y, top_y, phm_pct;
+    numeric bot_y, top_y;
     picture phm_pct;
-    save top_y, mid_y, bot_y;
-    numeric top_y, bot_y;
     if drv_bot_roots:
       bot_y:=xpart minmax_y[@]+min_clr_scl*min_clr[drv_sty]/2;
       top_y:=xpart minmax_y[tgt[@]];
@@ -1665,85 +1635,78 @@ vardef drv_build_root[]=
       bot_y:=ypart minmax_y[tgt[@]];
       top_y:=ypart minmax_y[@]-min_clr_scl*min_clr[drv_sty]/2;
     fi
-    mid_y:=(top_y+bot_y)/2;
-    phm_pth:=(0, (bot_y-top_y)/2)--(0, (top_y-bot_y)/2);
-    phm_pct:=phm_pth drv_styled phm_sty[@];
+    phm_pct:=((0, (bot_y-top_y)/2)--(0, (top_y-bot_y)/2))
+      drv_styled phm_sty[@];
     box_init phm[@] (phm_pct shifted ((width phm_pct)/2, 0));
-    phm[@].c=(xpart jdg[@].c, mid_y);
-    imin_x[@]:=min(imin_x[@], xpart phm[@].l);
-    imax_x[@]:=max(imax_x[@], xpart phm[@].r);
+    phm[@].c=(xpart jdg[@].c, (top_y+bot_y)/2);
+    nfr_min_x[@]:=min(nfr_min_x[@], xpart phm[@].l);
+    nfr_max_x[@]:=max(nfr_max_x[@], xpart phm[@].r);
     %
     % phantom steps labels
     %
     if known l_plb[@]:
       l_plb[@].r=phm[@].l shifted (-plb_skp[drv_sty], 0);
-      imin_x[@]:=min(imin_x[@], xpart l_plb[@].l);
+      nfr_min_x[@]:=min(nfr_min_x[@], xpart l_plb[@].l);
     fi
     if known r_plb[@]:
       r_plb[@].l=phm[@].r shifted ( plb_skp[drv_sty], 0);
-      imax_x[@]:=max(imax_x[@], xpart r_plb[@].r);
+      nfr_max_x[@]:=max(nfr_max_x[@], xpart r_plb[@].r);
     fi
   fi
   %
-  % smin_x & smax_x
+  % sub_min_x & sub_max_x
   %
-  smin_x[@]:=imin_x[@];
-  smax_x[@]:=imax_x[@];
+  sub_min_x[@]:=nfr_min_x[@];
+  sub_max_x[@]:=nfr_max_x[@];
   for prm_rnk=0 upto prm_num[@]-1:
-    smin_x[@]:=min(smin_x[@], smin_x[prm[@][prm_rnk]]);
-    smax_x[@]:=max(smax_x[@], smax_x[prm[@][prm_rnk]]);
+    sub_min_x[@]:=min(sub_min_x[@], sub_min_x[prm[@][prm_rnk]]);
+    sub_max_x[@]:=max(sub_max_x[@], sub_max_x[prm[@][prm_rnk]]);
   endfor
   %
   % delimiters
   %
   if known l_dlb[@] or known r_dlb[@]:
-    save idx, mmy, min_y, max_y;
-    numeric idx, min_y, max_y;
+    save mmy, min_y, max_y;
+    numeric min_y, max_y;
     pair mmy;
     mmy:=minmax_y[@];
     min_y:=xpart mmy;
     max_y:=ypart mmy;
     if known l_dlb[@]:
       box_init l_dlm[@] (delim l (max_y-min_y));
-      l_dlm[@].r=(smin_x[@], (max_y+min_y)/2);
+      l_dlm[@].r=(sub_min_x[@], (max_y+min_y)/2);
       l_dlb[@].r=l_dlm[@].l;
-      smin_x[@]:=xpart l_dlb[@].l;
+      sub_min_x[@]:=xpart l_dlb[@].l;
     fi
     if known r_dlb[@]:
       box_init r_dlm[@] (delim r (max_y-min_y));
-      r_dlm[@].l=(smax_x[@], (max_y+min_y)/2);
+      r_dlm[@].l=(sub_max_x[@], (max_y+min_y)/2);
       r_dlb[@].l=r_dlm[@].r;
-      smax_x[@]:=xpart r_dlb[@].r;
+      sub_max_x[@]:=xpart r_dlb[@].r;
     fi
   fi
   if (known l_dlb[@]) or boxed[@]:
+    save idx;
+    numeric idx;
     idx:=@;
     forever:
-      imin_x[idx]:=smin_x[@];
+      nfr_min_x[idx]:=sub_min_x[@];
       exitif unknown l_prm[idx];
       idx:=l_prm[idx];
     endfor
   fi
   if (known r_dlb[@]) or boxed[@]:
+    save idx;
+    numeric idx;
     idx:=@;
     forever:
-      imax_x[idx]:=smax_x[@];
+      nfr_max_x[idx]:=sub_max_x[@];
       exitif unknown r_prm[idx];
       idx:=r_prm[idx];
     endfor
   fi
 enddef;
 
-vardef drv_build=
-  if not drv_checked:
-    drv_check;
-  fi
-  for idx=0 upto root_num-1:
-    drv_build_root[root[idx]];
-  endfor
-  drv_built:=true;
-enddef;
-
 %
 % Freezing
 %
@@ -1766,28 +1729,31 @@ vardef drv_freeze_root[]=
 enddef;
 
 vardef drv_freeze=
-  if not drv_built:
-    drv_build;
+  if not drv_checked:
+    drv_check;
   fi
   save root_idx;
   numeric root_idx;
-  root_idx:=root[0];
-  if unknown iln[root_idx].c:
-    %
-    % default math axis
-    %
-    if drv_axis_ref="iln":
-      iln[root_idx].c=(0, axis_hg[drv_sty]);
-    else: % drv_axis_ref="jdg"
-      jdg[root_idx].c=(0, axis_hg[drv_sty]);
+  for root_rnk=0 upto root_num-1:
+    root_idx:=root[root_rnk];
+    drv_build_root[root_idx];
+    if unknown xpart jdg[root_idx].c:
+      if root_rnk=0:
+        xpart jdg[root_idx].c=0;
+      else:
+        sub_min_x[root_idx]=sub_max_x[root[root_rnk-1]]
+          +prm_skp_scl*prm_skp[drv_sty];
+      fi
     fi
-    drv_freeze_root[root_idx];
-  fi
-  for idx=1 upto root_num-1:
-    root_idx:=root[idx];
-    if unknown iln[root_idx].c:
-      smin_x[root_idx]=smax_x[root[idx-1]]+prm_skp_scl*prm_skp[drv_sty];
-      ypart iln[root_idx].c=ypart iln[root[idx-1]].c;
+    if unknown ypart jdg[root_idx].c:
+      %
+      % default math axis
+      %
+      if drv_axis_ref="iln":
+        ypart iln[root_idx].c=axis_hg[drv_sty];
+      else: % drv_axis_ref="jdg"
+        ypart jdg[root_idx].c=axis_hg[drv_sty];
+      fi
     fi
     drv_freeze_root[root_idx];
   endfor
@@ -1892,12 +1858,12 @@ vardef drv_tree=
   if not drv_frozen:
     drv_freeze;
   fi
-  for root_idx=0 upto root_num-1:
+  for root_rnk=0 upto root_num-1:
     if drv_proofmode_on:
-      drv_tree_addto pct (root[root_idx]) withcolor prf_clr;
-      prf_tree_addto pct (root[root_idx]);
+      drv_tree_addto pct (root[root_rnk]) withcolor prf_clr;
+      prf_tree_addto pct (root[root_rnk]);
     else:
-      drv_tree_addto pct (root[root_idx]);
+      drv_tree_addto pct (root[root_rnk]);
     fi
   endfor
   pct
@@ -1914,13 +1880,13 @@ vardef drv_bbox[]=
     if known l_dlm[@].r:
       xpart l_dlm[@].r
     else:
-      smin_x[@]
+      sub_min_x[@]
     fi-jdg_skp_scl*jdg_skp[jdg_sty[drv_sty]];
   max_x:=
     if known r_dlm[@].l:
       xpart l_dlm[@].l
     else:
-      smax_x[@]
+      sub_max_x[@]
     fi+jdg_skp_scl*jdg_skp[jdg_sty[drv_sty]];
   mmy:=minmax_y[@];
   min_y:=xpart mmy;
@@ -2158,7 +2124,8 @@ vardef drv_axis_reference suffix ref_sfx=
   string ref_str;
   ref_str:=str ref_sfx;
   if (ref_str<>"iln") and (ref_str<>"jdg"):
-    drv_errhelp "Valid identifiers are iln (inference line axis) and"&
+    drv_errhelp "Valid identifiers are"&
+      " iln (inference line axis) and"&
       " jdg (judgment math-axis).";
     drv_errmessage (ref_str&" is not a valid reference identifier");
   else:
@@ -2168,9 +2135,9 @@ enddef;
 
 vardef drv_delimiter (suffix pos_sfx) (expr dlm_str)=
   if check_position_left (pos_sfx, true):
-    drv_l_dlm:=dlm_str;
+    drv_ldlm_str:=dlm_str;
   else:
-    drv_r_dlm:=dlm_str;
+    drv_rdlm_str:=dlm_str;
   fi
 enddef;