path: root/Build/source/texk/web2c/luatexdir/tex/texmath.c

/*

Copyright 2008-2010 Taco Hoekwater <taco@luatex.org>

This file is part of LuaTeX.

LuaTeX is free software; you can redistribute it and/or modify it under the terms
of the GNU General Public License as published by the Free Software Foundation;
either version 2 of the License, or (at your option) any later version.

LuaTeX is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.

You should have received a copy of the GNU General Public License along with
LuaTeX; if not, see <http://www.gnu.org/licenses/>.

*/

#include "ptexlib.h"

#define mode     mode_par
#define tail     tail_par
#define head     head_par
#define dir_save dirs_par

/*tex

    Concerning display skips, \TEX\ normally always inserts before and only after
    when larger than zero. THis can ow be controlled with |\mathdisplayskipmode|:

    \starttabulate
    \NC 0 \NC normal \TEX \NC \NR
    \NC 1 \NC always      \NC \NR
    \NC 2 \NC non-zero    \NC \NR
    \NC 3 \NC ignore      \NC \NR
    \stoptabulate

*/

#define back_error(A,B) do {                    \
    OK_to_interrupt=false;                      \
    back_input();                               \
    OK_to_interrupt=true;                       \
    tex_error(A,B);                             \
  } while (0)

int scan_math(pointer, int);
int scan_math_style(pointer, int);
pointer fin_mlist(pointer);

/*tex

    When \TeX\ reads a formula that is enclosed between \.\$'s, it constructs an
    {\sl mlist}, which is essentially a tree structure representing that formula.
    An mlist is a linear sequence of items, but we can regard it as a tree
    structure because mlists can appear within mlists. For example, many of the
    entries can be subscripted or superscripted, and such ``scripts'' are mlists
    in their own right.

    An entire formula is parsed into such a tree before any of the actual
    typesetting is done, because the current style of type is usually not known
    until the formula has been fully scanned. For example, when the formula
    `\.{\$a+b \\over c+d\$}' is being read, there is no way to tell that
    `\.{a+b}' will be in script size until `\.{\\over}' has appeared.

    During the scanning process, each element of the mlist being built is
    classified as a relation, a binary operator, an open parenthesis, etc., or as
    a construct like `\.{\\sqrt}' that must be built up. This classification
    appears in the mlist data structure.

    After a formula has been fully scanned, the mlist is converted to an hlist so
    that it can be incorporated into the surrounding text. This conversion is
    controlled by a recursive procedure that decides all of the appropriate
    styles by a ``top-down'' process starting at the outermost level and working
    in towards the subformulas. The formula is ultimately pasted together using
    combinations of horizontal and vertical boxes, with glue and penalty nodes
    inserted as necessary.

    An mlist is represented internally as a linked list consisting chiefly of
    ``noads'' (pronounced ``no-adds''), to distinguish them from the somewhat
    similar ``nodes'' in hlists and vlists. Certain kinds of ordinary nodes are
    allowed to appear in mlists together with the noads; \TeX\ tells the
    difference by means of the |type| field, since a noad's |type| is always
    greater than that of a node. An mlist does not contain character nodes, hlist
    nodes, vlist nodes, math nodes or unset nodes; in particular, each mlist item
    appears in the variable-size part of |mem|, so the |type| field is always
    present.

    Each noad is five or more words long. The first word contains the |type| and
    |subtype| and |link| fields that are already so familiar to us; the second
    contains the attribute list pointer, and the third, fourth an fifth words are
    called the noad's |nucleus|, |subscr|, and |supscr| fields. (This use of a
    combined attribute list is temporary. Eventually, each of fields need their
    own list)

    Consider, for example, the simple formula `\.{\$x\^2\$}', which would be
    parsed into an mlist containing a single element called an |ord_noad|. The
    |nucleus| of this noad is a representation of `\.x', the |subscr| is empty,
    and the |supscr| is a representation of `\.2'.

    The |nucleus|, |subscr|, and |supscr| fields are further broken into
    subfields. If |p| points to a noad, and if |q| is one of its principal fields
    (e.g., |q=subscr(p)|), |q=null| indicates a field with no value (the
    corresponding attribute of noad |p| is not present). Otherwise, there are
    several possibilities for the subfields, depending on the |type| of |q|.

    \startitemize

        \startitem
            |type(q)=math_char_node| means that |math_fam(q)| refers to one of
            the sixteen font families, and |character(q)| is the number of a
            character within a font of that family, as in a character node.
        \stopitem

        \startitem
            |type(q)=math_text_char_node| is similar, but the character is
            unsubscripted and unsuperscripted and it is followed immediately by
            another character from the same font. (This |type| setting appears
            only briefly during the processing; it is used to suppress unwanted
            italic corrections.)
        \stopitem

        \startitem
            |type(q)=sub_box_node| means that |math_list(q)| points to a box node
            (either an |hlist_node| or a |vlist_node|) that should be used as the
            value of the field. The |shift_amount| in the subsidiary box node is
            the amount by which that box will be shifted downward.
        \stopitem

        \startitem
            |type(q)=sub_mlist_node| means that |math_list(q)| points to an
            mlist; the mlist must be converted to an hlist in order to obtain the
            value of this field.
        \stopitem

        \startitem
            In the latter case, we might have |math_list(q)=null|. This is not
            the same as |q=null|; for example, `\.{\$P\_\{\}\$}' and `\.{\$P\$}'
            produce different results (the former will not have the ``italic
            correction'' added to the width of |P|, but the ``script skip'' will
            be added).
        \stopitem

    \startitemize

*/

static void unsave_math(void)
{
    unsave();
    decr(save_ptr);
    flush_node_list(text_dir_ptr);
    assert(saved_type(0) == saved_textdir);
    text_dir_ptr = saved_value(0);
}

/*tex

    Sometimes it is necessary to destroy an mlist. The following subroutine
    empties the current list, assuming that |abs(mode)=mmode|.

*/

void flush_math(void)
{
    flush_node_list(vlink(head));
    flush_node_list(incompleat_noad_par);
    vlink(head) = null;
    tail = head;
    incompleat_noad_par = null;
}

/*tex Before we can do anything in math mode, we need fonts. */

#define MATHFONTSTACK  8
#define MATHFONTDEFAULT 0

static sa_tree math_fam_head = NULL;

int fam_fnt(int fam_id, int size_id)
{
    int n = fam_id + (256 * size_id);
    return (int) get_sa_item(math_fam_head, n).int_value;
}

void def_fam_fnt(int fam_id, int size_id, int f, int lvl)
{
    int n = fam_id + (256 * size_id);
    sa_tree_item sa_value = { 0 };
    sa_value.int_value = f;
    set_sa_item(math_fam_head, n, sa_value, lvl);
    fixup_math_parameters(fam_id, size_id, f, lvl);
    if (tracing_assigns_par > 1) {
        begin_diagnostic();
        tprint("{assigning");
        print_char(' ');
        print_cmd_chr(def_family_cmd, size_id);
        print_int(fam_id);
        print_char('=');
        print_font_identifier(fam_fnt(fam_id, size_id));
        print_char('}');
        end_diagnostic(false);
    }
}

static void unsave_math_fam_data(int gl)
{
    sa_stack_item st;
    if (math_fam_head->stack == NULL)
        return;
    while (math_fam_head->stack_ptr > 0 &&
           abs(math_fam_head->stack[math_fam_head->stack_ptr].level)
           >= (int) gl) {
        st = math_fam_head->stack[math_fam_head->stack_ptr];
        if (st.level > 0) {
            rawset_sa_item(math_fam_head, st.code, st.value);
            /*tex Now do a trace message, if requested. */
            if (tracing_restores_par > 1) {
                int size_id = st.code / 256;
                int fam_id = st.code % 256;
                begin_diagnostic();
                tprint("{restoring");
                print_char(' ');
                print_cmd_chr(def_family_cmd, size_id);
                print_int(fam_id);
                print_char('=');
                print_font_identifier(fam_fnt(fam_id, size_id));
                print_char('}');
                end_diagnostic(false);
            }
        }
        (math_fam_head->stack_ptr)--;
    }
}

/*tex Parameters */

#define MATHPARAMSTACK  8
#define MATHPARAMDEFAULT undefined_math_parameter

static sa_tree math_param_head = NULL;

void def_math_param(int param_id, int style_id, scaled value, int lvl)
{
    int n = param_id + (256 * style_id);
    sa_tree_item sa_value = { 0 };
    sa_value.int_value = (int) value;
    set_sa_item(math_param_head, n, sa_value, lvl);
    if (tracing_assigns_par > 1) {
        begin_diagnostic();
        tprint("{assigning");
        print_char(' ');
        print_cmd_chr(set_math_param_cmd, param_id);
        print_cmd_chr(math_style_cmd, style_id);
        print_char('=');
        print_int(value);
        print_char('}');
        end_diagnostic(false);
    }
}

scaled get_math_param(int param_id, int style_id)
{
    int n = param_id + (256 * style_id);
    return (scaled) get_sa_item(math_param_head, n).int_value;
}

static void unsave_math_param_data(int gl)
{
    sa_stack_item st;
    if (math_param_head->stack == NULL)
        return;
    while (math_param_head->stack_ptr > 0 &&
           abs(math_param_head->stack[math_param_head->stack_ptr].level)
           >= (int) gl) {
        st = math_param_head->stack[math_param_head->stack_ptr];
        if (st.level > 0) {
            rawset_sa_item(math_param_head, st.code, st.value);
            /*tex Do a trace message, if requested. */
            if (tracing_restores_par > 1) {
                int param_id = st.code % 256;
                int style_id = st.code / 256;
                begin_diagnostic();
                tprint("{restoring");
                print_char(' ');
                print_cmd_chr(set_math_param_cmd, param_id);
                print_cmd_chr(math_style_cmd, style_id);
                print_char('=');
                print_int(get_math_param(param_id, style_id));
                print_char('}');
                end_diagnostic(false);
            }
        }
        (math_param_head->stack_ptr)--;
    }
}

/*tex Saving and unsaving of both: */

void unsave_math_data(int gl)
{
    unsave_math_fam_data(gl);
    unsave_math_param_data(gl);
}

/*tex Dumping and undumping: */

void dump_math_data(void)
{
    sa_tree_item sa_value = { 0 };
    if (math_fam_head == NULL) {
        sa_value.int_value = MATHFONTDEFAULT;
        math_fam_head = new_sa_tree(MATHFONTSTACK, 1, sa_value);
    }
    dump_sa_tree(math_fam_head, "mathfonts");
    if (math_param_head == NULL) {
        sa_value.int_value = MATHPARAMDEFAULT;
        math_param_head = new_sa_tree(MATHPARAMSTACK, 1, sa_value);
    }
    dump_sa_tree(math_param_head, "mathparameters");
}

void undump_math_data(void)
{
    math_fam_head = undump_sa_tree("mathfonts");
    math_param_head = undump_sa_tree("mathparameters");
}

void initialize_math(void)
{
    sa_tree_item sa_value = { 0 };
    if (math_fam_head == NULL) {
        sa_value.int_value = MATHFONTDEFAULT;
        math_fam_head = new_sa_tree(MATHFONTSTACK, 1, sa_value);
    }
    if (math_param_head == NULL) {
        sa_value.int_value = MATHPARAMDEFAULT;
        math_param_head = new_sa_tree(MATHPARAMSTACK, 1, sa_value);
        initialize_math_spacing();
    }
    return;
}

/*tex

    Each portion of a formula is classified as Ord, Op, Bin, Rel, Ope, Clo, Pun,
    or Inn, for purposes of spacing and line breaking. An |ord_noad|, |op_noad|,
    |bin_noad|, |rel_noad|, |open_noad|, |close_noad|, |punct_noad|, or
    |inner_noad| is used to represent portions of the various types. For example,
    an `\.=' sign in a formula leads to the creation of a |rel_noad| whose
    |nucleus| field is a representation of an equals sign (usually |fam=0|,
    |character=075|). A formula preceded by \.{\\mathrel} also results in a
    |rel_noad|. When a |rel_noad| is followed by an |op_noad|, say, and possibly
    separated by one or more ordinary nodes (not noads), \TeX\ will insert a
    penalty node (with the current |rel_penalty|) just after the formula that
    corresponds to the |rel_noad|, unless there already was a penalty immediately
    following; and a ``thick space'' will be inserted just before the formula
    that corresponds to the |op_noad|.

    A noad of type |ord_noad|, |op_noad|, \dots, |inner_noad| usually has a
    |subtype=normal|. The only exception is that an |op_noad| might have
    |subtype=limits| or |no_limits|, if the normal positioning of limits has been
    overridden for this operator.

    A |radical_noad| also has a |left_delimiter| field, which usually represents
    a square root sign.

    A |fraction_noad| has a |right_delimiter| field as well as a
    |left_delimiter|.

    Delimiter fields have four subfields called |small_fam|, |small_char|,
    |large_fam|, |large_char|. These subfields represent variable-size delimiters
    by giving the ``small'' and ``large'' starting characters, as explained in
    Chapter~17 of {\sl The \TeX book}.

    A |fraction_noad| is actually quite different from all other noads. It has
    |thickness|, |denominator|, and |numerator| fields instead of |nucleus|,
    |subscr|, and |supscr|. The |thickness| is a scaled value that tells how
    thick to make a fraction rule; however, the special value |default_code| is
    used to stand for the |default_rule_thickness| of the current size. The
    |numerator| and |denominator| point to mlists that define a fraction; we
    always have $$\hbox{|type(numerator)=type(denominator)=sub_mlist|}.$$ The
    |left_delimiter| and |right_delimiter| fields specify delimiters that will be
    placed at the left and right of the fraction. In this way, a |fraction_noad|
    is able to represent all of \TeX's operators \.{\\over}, \.{\\atop},
    \.{\\above}, \.{\\overwithdelims}, \.{\\atopwithdelims}, and
    \.{\\abovewithdelims}.

    The |new_noad| function creates an |ord_noad| that is completely null

*/

pointer new_noad(void)
{
    pointer p;
    p = new_node(simple_noad, ord_noad_type);
    /*tex All noad fields are zero after this. */
    return p;
}

pointer new_sub_box(pointer curbox)
{
    pointer p, q;
    p = new_noad();
    q = new_node(sub_box_node, 0);
    nucleus(p) = q;
    math_list(nucleus(p)) = curbox;
    return p;
}

/*tex

    A few more kinds of noads will complete the set: An |under_noad| has its
    nucleus underlined; an |over_noad| has it overlined. An |accent_noad| places
    an accent over its nucleus; the accent character appears as
    |math_fam(accent_chr(p))| and |math_character(accent_chr(p))|. A
    |vcenter_noad| centers its nucleus vertically with respect to the axis of the
    formula; in such noads we always have |type(nucleus(p))=sub_box|.

    And finally, we have the |fence_noad| type, to implement \TeX's \.{\\left}
    and \.{\\right} as well as eTeX's \.{\\middle}. The |nucleus| of such noads
    is replaced by a |delimiter| field; thus, for example, `\.{\\left(}' produces
    a |fence_noad| such that |delimiter(p)| holds the family and character codes
    for all left parentheses. A |fence_noad| of subtype |left_noad_side| never
    appears in an mlist except as the first element, and a |fence_noad| with
    subtype |right_noad_side| never appears in an mlist except as the last
    element; furthermore, we either have both a |left_noad_side| and a
    |right_noad_side|, or neither one is present.

    Math formulas can also contain instructions like \.{\\textstyle} that
    override \TeX's normal style rules. A |style_node| is inserted into the data
    structure to record such instructions; it is three words long, so it is
    considered a node instead of a noad. The |subtype| is either |display_style|
    or |text_style| or |script_style| or |script_script_style|. The second and
    third words of a |style_node| are not used, but they are present because a
    |choice_node| is converted to a |style_node|.

    \TeX\ uses even numbers 0, 2, 4, 6 to encode the basic styles
    |display_style|, \dots, |script_script_style|, and adds~1 to get the
    ``cramped'' versions of these styles. This gives a numerical order that is
    backwards from the convention of Appendix~G in {\sl The \TeX book\/}; i.e., a
    smaller style has a larger numerical value.

*/

const char *math_style_names[] = {
    "display", "crampeddisplay",
    "text", "crampedtext",
    "script", "crampedscript",
    "scriptscript", "crampedscriptscript",
    NULL
};

const char *math_param_names[] = {
    "quad", "axis", "operatorsize",
    "overbarkern", "overbarrule", "overbarvgap",
    "underbarkern", "underbarrule", "underbarvgap",
    "radicalkern", "radicalrule", "radicalvgap",
    "radicaldegreebefore", "radicaldegreeafter", "radicaldegreeraise",
    "stackvgap", "stacknumup", "stackdenomdown",
    "fractionrule", "fractionnumvgap", "fractionnumup",
    "fractiondenomvgap", "fractiondenomdown", "fractiondelsize",
    "skewedfractionhgap", "skewedfractionvgap",
    "limitabovevgap", "limitabovebgap", "limitabovekern",
    "limitbelowvgap", "limitbelowbgap", "limitbelowkern",
    "nolimitsubfactor", "nolimitsupfactor", /* bonus */
    "underdelimitervgap", "underdelimiterbgap",
    "overdelimitervgap", "overdelimiterbgap",
    "subshiftdrop", "supshiftdrop", "subshiftdown",
    "subsupshiftdown", "subtopmax", "supshiftup",
    "supbottommin", "supsubbottommax", "subsupvgap",
    "spaceafterscript", "connectoroverlapmin",
    "ordordspacing", "ordopspacing", "ordbinspacing", "ordrelspacing",
    "ordopenspacing", "ordclosespacing", "ordpunctspacing", "ordinnerspacing",
    "opordspacing", "opopspacing", "opbinspacing", "oprelspacing",
    "opopenspacing", "opclosespacing", "oppunctspacing", "opinnerspacing",
    "binordspacing", "binopspacing", "binbinspacing", "binrelspacing",
    "binopenspacing", "binclosespacing", "binpunctspacing", "bininnerspacing",
    "relordspacing", "relopspacing", "relbinspacing", "relrelspacing",
    "relopenspacing", "relclosespacing", "relpunctspacing", "relinnerspacing",
    "openordspacing", "openopspacing", "openbinspacing", "openrelspacing",
    "openopenspacing", "openclosespacing", "openpunctspacing",
    "openinnerspacing",
    "closeordspacing", "closeopspacing", "closebinspacing", "closerelspacing",
    "closeopenspacing", "closeclosespacing", "closepunctspacing",
    "closeinnerspacing",
    "punctordspacing", "punctopspacing", "punctbinspacing", "punctrelspacing",
    "punctopenspacing", "punctclosespacing", "punctpunctspacing",
    "punctinnerspacing",
    "innerordspacing", "inneropspacing", "innerbinspacing", "innerrelspacing",
    "inneropenspacing", "innerclosespacing", "innerpunctspacing",
    "innerinnerspacing",
    NULL
};

pointer new_style(small_number s)
{
    m_style = s;
    return new_node(style_node, s);
}

/*tex

    Finally, the \.{\\mathchoice} primitive creates a |choice_node|, which has
    special subfields |display_mlist|, |text_mlist|, |script_mlist|, and
    |script_script_mlist| pointing to the mlists for each style.

*/

static pointer new_choice(void)
{
    return new_node(choice_node, 0);
}

/*tex

    Let's consider now the previously unwritten part of |show_node_list| that
    displays the things that can only be present in mlists; this program
    illustrates how to access the data structures just defined.

    In the context of the following program, |p| points to a node or noad that
    should be displayed, and the current string contains the ``recursion
    history'' that leads to this point. The recursion history consists of a dot
    for each outer level in which |p| is subsidiary to some node, or in which |p|
    is subsidiary to the |nucleus| field of some noad; the dot is replaced by
    `\.\_' or `\.\^' or `\./' or `\.\\' if |p| is descended from the |subscr| or
    |supscr| or |denominator| or |numerator| fields of noads. For example, the
    current string would be `\.{.\^.\_/}' if |p| points to the |ord_noad| for |x|
    in the (ridiculous) formula `\.{\$\\sqrt\{a\^\{\\mathinner\{b\_\{c\\over
    x+y\}\}\}\}\$}'.

*/

void display_normal_noad(pointer p);
void display_fence_noad(pointer p);
void display_fraction_noad(pointer p);

void show_math_node(pointer p)
{
    switch (type(p)) {
        case style_node:
            print_cmd_chr(math_style_cmd, subtype(p));
            break;
        case choice_node:
            tprint_esc("mathchoice");
            append_char('D');
            show_node_list(display_mlist(p));
            flush_char();
            append_char('T');
            show_node_list(text_mlist(p));
            flush_char();
            append_char('S');
            show_node_list(script_mlist(p));
            flush_char();
            append_char('s');
            show_node_list(script_script_mlist(p));
            flush_char();
            break;
        case simple_noad:
        case radical_noad:
        case accent_noad:
            display_normal_noad(p);
            break;
        case fence_noad:
            display_fence_noad(p);
            break;
        case fraction_noad:
            display_fraction_noad(p);
            break;
        default:
            tprint("Unknown node type!");
            break;
    }
}

/*tex Here are some simple routines used in the display of noads. */

static void print_fam_and_char(pointer p)
{
    tprint_esc("fam");
    print_int(math_fam(p));
    print_char(' ');
    print(math_character(p));
}

static void print_delimiter(pointer p)
{
    int a;
    if (delimiteroptionset(p)) {
        tprint(" [ ");
        if (delimiteraxis(p))
            tprint("axis ");
        if (delimiternoaxis(p))
            tprint("noaxis ");
        if (delimiterexact(p))
            tprint("exact ");
        tprint("]");
    }
    if (delimiterheight(p)) {
        tprint("height=");
        print_scaled(delimiterheight(p));
        tprint(" ");
    }
    if (delimiterdepth(p)) {
        tprint("depth=");
        print_scaled(delimiterdepth(p));
        tprint(" ");
    }
    if (delimiterclass(p)) {
        tprint("class=");
        print_int(delimiterclass(p));
        tprint(" ");
    }
    if (small_fam(p) < 0) {
        /*tex This should never happen. */
        print_int(-1);
    } else if (small_fam(p) < 16 && large_fam(p) < 16 && small_char(p) < 256 && large_char(p) < 256) {
        /*tex Traditional tex style. */
        a = small_fam(p) * 256 + small_char(p);
        a = a * 0x1000 + large_fam(p) * 256 + large_char(p);
        print_qhex(a);
    } else if ((large_fam(p) == 0 && large_char(p) == 0) || small_char(p) > 65535 || large_char(p) > 65535) {
        /*tex \LUATEX\ style. */
        print_qhex(small_fam(p));
        print_qhex(small_char(p));
    }
}

/*tex

    The next subroutine will descend to another level of recursion when a
    subsidiary mlist needs to be displayed. The parameter |c| indicates what
    character is to become part of the recursion history. An empty mlist is
    distinguished from a missing field, because these are not equivalent (as
    explained above).

*/

static void print_subsidiary_data(pointer p, ASCII_code c)
{
    if ((int) cur_length >= depth_threshold) {
        if (p != null)
            tprint(" []");
    } else {
        /*tex Include |c| in the recursion history. */
        append_char(c);
        if (p != null) {
            switch (type(p)) {
            case math_char_node:
                print_ln();
                print_current_string();
                print_fam_and_char(p);
                break;
            case sub_box_node:
                show_node_list(math_list(p));
                break;
            case sub_mlist_node:
                if (math_list(p) == null) {
                    print_ln();
                    print_current_string();
                    tprint("{}");
                } else {
                    show_node_list(math_list(p));
                }
                break;
            }
        }
        /*tex Remove |c| from the recursion history. */
        flush_char();
    }
}

void display_normal_noad(pointer p)
{
    switch (type(p)) {
    case simple_noad:
        switch (subtype(p)) {
            case ord_noad_type:
                tprint_esc("mathord");
                break;
            case op_noad_type_normal:
            case op_noad_type_limits:
            case op_noad_type_no_limits:
                tprint_esc("mathop");
                if (subtype(p) == op_noad_type_limits)
                    tprint_esc("limits");
                else if (subtype(p) == op_noad_type_no_limits)
                    tprint_esc("nolimits");
                break;
            case bin_noad_type:
                tprint_esc("mathbin");
                break;
            case rel_noad_type:
                tprint_esc("mathrel");
                break;
            case open_noad_type:
                tprint_esc("mathopen");
                break;
            case close_noad_type:
                tprint_esc("mathclose");
                break;
            case punct_noad_type:
                tprint_esc("mathpunct");
                break;
            case inner_noad_type:
                tprint_esc("mathinner");
                break;
            case over_noad_type:
                tprint_esc("overline");
                break;
            case under_noad_type:
                tprint_esc("underline");
                break;
            case vcenter_noad_type:
                tprint_esc("vcenter");
                break;
            default:
                tprint("<unknown noad type!>");
                break;
        }
        break;
    case radical_noad:
        if (subtype(p) == 7)
            tprint_esc("Uhextensible");
        else if (subtype(p) == 6)
            tprint_esc("Udelimiterover");
        else if (subtype(p) == 5)
            tprint_esc("Udelimiterunder");
        else if (subtype(p) == 4)
            tprint_esc("Uoverdelimiter");
        else if (subtype(p) == 3)
            tprint_esc("Uunderdelimiter");
        else if (subtype(p) == 2)
            tprint_esc("Uroot");
        else
            tprint_esc("radical");
        print_delimiter(left_delimiter(p));
        if (degree(p) != null) {
            print_subsidiary_data(degree(p), '/');
        }
        if (radicalwidth(p)) {
            tprint("width=");
            print_scaled(radicalwidth(p));
            tprint(" ");
        }
        if (radicaloptionset(p)) {
            tprint(" [ ");
            if (radicalexact(p))
                tprint("exact ");
            if (radicalleft(p))
                tprint("left ");
            if (radicalmiddle(p))
                tprint("middle ");
            if (radicalright(p))
                tprint("right ");
            tprint("]");
        }
        break;
    case accent_noad:
       if (top_accent_chr(p) != null) {
           if (bot_accent_chr(p) != null) {
               tprint_esc("Umathaccent both");
           } else {
               tprint_esc("Umathaccent");
           }
        } else if (bot_accent_chr(p) != null) {
            tprint_esc("Umathaccent bottom");
        } else {
            tprint_esc("Umathaccent overlay");
        }
        if (accentfraction(p)) {
            tprint(" fraction=");
            print_int(accentfraction(p));
            tprint(" ");
        }
        switch (subtype(p)) {
            case 0:
                if (top_accent_chr(p) != null) {
                    if (bot_accent_chr(p) != null) {
                        print_fam_and_char(top_accent_chr(p));
                        print_fam_and_char(bot_accent_chr(p));
                    } else {
                        print_fam_and_char(top_accent_chr(p));
                    }
                } else if (bot_accent_chr(p) != null) {
                    print_fam_and_char(bot_accent_chr(p));
                } else {
                    print_fam_and_char(overlay_accent_chr(p));
                }
                break;
            case 1:
                if (top_accent_chr(p) != null) {
                    tprint(" fixed ");
                    print_fam_and_char(top_accent_chr(p));
                    if (bot_accent_chr(p) != null) {
                        print_fam_and_char(bot_accent_chr(p));
                    }
                } else {
                    confusion("display_accent_noad");
                }
                break;
            case 2:
                if (bot_accent_chr(p) != null) {
                    if (top_accent_chr(p) != null) {
                        print_fam_and_char(top_accent_chr(p));
                    }
                    tprint(" fixed ");
                    print_fam_and_char(bot_accent_chr(p));
                } else{
                    confusion("display_accent_noad");
                }
                break;
            case 3:
                if (top_accent_chr(p) != null && bot_accent_chr(p) != null) {
                    tprint(" fixed ");
                    print_fam_and_char(top_accent_chr(p));
                    tprint(" fixed ");
                    print_fam_and_char(bot_accent_chr(p));
                } else {
                    confusion("display_accent_noad");
                }
                break;
            }
        break;
    }
    print_subsidiary_data(nucleus(p), '.');
    print_subsidiary_data(supscr(p), '^');
    print_subsidiary_data(subscr(p), '_');
}

void display_fence_noad(pointer p)
{
    if (subtype(p) == right_noad_side)
        tprint_esc("right");
    else if (subtype(p) == left_noad_side)
        tprint_esc("left");
    else
        tprint_esc("middle");
    print_delimiter(delimiter(p));
}

void display_fraction_noad(pointer p)
{
    tprint_esc("fraction, thickness ");
    if (thickness(p) == default_code)
        tprint("= default");
    else
        print_scaled(thickness(p));
    if ((left_delimiter(p) != null) &&
        ((small_fam(left_delimiter(p)) != 0) || (small_char(left_delimiter(p)) != 0) ||
         (large_fam(left_delimiter(p)) != 0) || (large_char(left_delimiter(p)) != 0))) {
        tprint(", left-delimiter ");
        print_delimiter(left_delimiter(p));
    }
    if ((right_delimiter(p) != null) &&
        ((small_fam(right_delimiter(p)) != 0) || (small_char(right_delimiter(p)) != 0) ||
         (large_fam(right_delimiter(p)) != 0) || (large_char(right_delimiter(p)) != 0))) {
        tprint(", right-delimiter ");
        print_delimiter(right_delimiter(p));
    }
    print_subsidiary_data(numerator(p), '\\');
    print_subsidiary_data(denominator(p), '/');
}

/*tex

    The routines that \TeX\ uses to create mlists are similar to those we have
    just seen for the generation of hlists and vlists. But it is necessary to
    make ``noads'' as well as nodes, so the reader should review the discussion
    of math mode data structures before trying to make sense out of the following
    program.

    Here is a little routine that needs to be done whenever a subformula is about
    to be processed. The parameter is a code like |math_group|.

*/

static void new_save_level_math(group_code c)
{
    set_saved_record(0, saved_textdir, 0, text_dir_ptr);
    text_dir_ptr = new_dir(math_direction_par);
    incr(save_ptr);
    new_save_level(c);
    eq_word_define(int_base + body_direction_code, math_direction_par);
    eq_word_define(int_base + par_direction_code, math_direction_par);
    eq_word_define(int_base + text_direction_code, math_direction_par);
}

static void push_math(group_code c, int mstyle)
{
    if (math_direction_par != text_direction_par)
        dir_math_save = true;
    push_nest();
    mode = -mmode;
    incompleat_noad_par = null;
    m_style = mstyle;
    new_save_level_math(c);
}

static void enter_ordinary_math(void)
{
    push_math(math_shift_group, text_style);
    eq_word_define(int_base + cur_fam_code, -1);
    if (every_math_par != null)
        begin_token_list(every_math_par, every_math_text);
}

void enter_display_math(void);

/*tex

    We get into math mode from horizontal mode when a `\.\$' (i.e., a
    |math_shift| character) is scanned. We must check to see whether this `\.\$'
    is immediately followed by another, in case display math mode is called for.

*/

void init_math(void)
{
    if (cur_cmd == math_shift_cmd) {
        /*tex |get_x_token| would fail on \.{\\ifmmode}\thinspace! */
        get_token();
        if ((cur_cmd == math_shift_cmd) && (mode > 0)) {
            enter_display_math();
        } else {
            back_input();
            enter_ordinary_math();
        }
    } else if (cur_cmd == math_shift_cs_cmd && cur_chr == display_style && (mode > 0)) {
        enter_display_math();
    } else if (cur_cmd == math_shift_cs_cmd && cur_chr == text_style) {
        enter_ordinary_math();
    } else {
        you_cant();
    }
}

/*tex

    We get into ordinary math mode from display math mode when `\.{\\eqno}' or
    `\.{\\leqno}' appears. In such cases |cur_chr| will be 0 or~1, respectively;
    the value of |cur_chr| is placed onto |save_stack| for safe keeping.

    When \TeX\ is in display math mode, |cur_group=math_shift_group|, so it is
    not necessary for the |start_eq_no| procedure to test for this condition.

*/

void start_eq_no(void)
{
    set_saved_record(0, saved_eqno, 0, cur_chr);
    incr(save_ptr);
    enter_ordinary_math();
}

/*tex

    Subformulas of math formulas cause a new level of math mode to be entered, on
    the semantic nest as well as the save stack. These subformulas arise in
    several ways: (1)~A left brace by itself indicates the beginning of a
    subformula that will be put into a box, thereby freezing its glue and
    preventing line breaks. (2)~A subscript or superscript is treated as a
    subformula if it is not a single character; the same applies to the nucleus
    of things like \.{\\underline}. (3)~The \.{\\left} primitive initiates a
    subformula that will be terminated by a matching \.{\\right}. The group codes
    placed on |save_stack| in these three cases are |math_group|, |math_group|,
    and |math_left_group|, respectively.

    Here is the code that handles case (1); the other cases are not quite as
    trivial, so we shall consider them later.

*/

void math_left_brace(void)
{
    pointer q;
    tail_append(new_noad());
    q = new_node(math_char_node, 0);
    nucleus(tail) = q;
    back_input();
    (void) scan_math(nucleus(tail), m_style);
}

/*tex

    If the inline directions of \.{\\pardir} and \.{\\mathdir} are opposite, then
    this function will return true. Discovering that fact is somewhat odd because
    it needs traversal of the |save_stack|. The occurance of displayed equations
    is weird enough that this is probably still better than having yet another
    field in the |input_stack| structures.

    None of this makes much sense if the inline direction of either one of
    \.{\\pardir} or \.{\\mathdir} is vertical, but in that case the current math
    machinery is ill suited anyway so I do not bother to test that.

*/

static boolean math_and_text_reversed_p(void)
{
    int i = save_ptr - 1;
    while (save_type(i) != level_boundary)
        i--;
    while (i < save_ptr) {
        if (save_type(i) == restore_old_value &&
            save_value(i) == int_base + par_direction_code) {
            if (textdir_opposite(math_direction_par, save_value(i - 1)))
                return true;
        }
        i++;
    }
    return false;
}

/*tex

    When we enter display math mode, we need to call |line_break| to process the
    partial paragraph that has just been interrupted by the display. Then we can
    set the proper values of |display_width| and |display_indent| and
    |pre_display_size|.

*/

void enter_display_math(void)
{
    /*tex new or partial |pre_display_size| */
    scaled w;
    /*tex new |display_width| */
    scaled l;
    /*tex new |display_indent| */
    scaled s;
    pointer p;
    /*tex scope of paragraph shape specification */
    int n;
    /*tex

        `\.{\\noindent\$\$}' or `\.{\$\${ }\$\$}' or the 2nd of \.{\$\${ }\$\$}
        \.{\$\${ }\$\$}

    */
    if (head == tail ||
        (vlink(head) == tail &&
         type(tail) == local_par_node && vlink(tail) == null)) {
        if (vlink(head) == tail) {
            /*tex

                |resume_after_display| inserts a |local_par_node|, but if there
                is another display immediately following, we have to get rid of
                that node.

            */
            flush_node(tail);
        }
        pop_nest();
        w = -max_dimen;
    } else {
        line_break(true, math_shift_group);
        w = actual_box_width(just_box, x_over_n(quad(get_cur_font()),1000) * math_pre_display_gap_factor_par);
    }
    /*tex

        Now we are in vertical mode, working on the list that will contain the
        display. A displayed equation is considered to be three lines long, so we
        calculate the length and offset of line number |prev_graf+2|.

    */
    if (par_shape_par_ptr == null) {
        if ((hang_indent_par != 0) && (((hang_after_par >= 0) && (prev_graf_par + 2 > hang_after_par)) || (prev_graf_par + 1 < -hang_after_par))) {
            halfword used_hang_indent = swap_hang_indent(hang_indent_par);
            l = hsize_par - abs(used_hang_indent);
            if (used_hang_indent > 0)
                s = used_hang_indent;
            else
                s = 0;
        } else {
            l = hsize_par;
            s = 0;
        }
    } else {
        n = vinfo(par_shape_par_ptr + 1);
        if (prev_graf_par + 2 >= n)
            p = par_shape_par_ptr + 2 * n + 1;
        else
            p = par_shape_par_ptr + 2 * (prev_graf_par + 2) + 1;
        s = varmem[(p - 1)].cint;
        l = varmem[p].cint;
        s = swap_parshape_indent(s,l);
    }
    push_math(math_shift_group, display_style);
    mode = mmode;
    eq_word_define(int_base + cur_fam_code, -1);
    eq_word_define(dimen_base + pre_display_size_code, w);
    eq_word_define(dimen_base + display_width_code, l);
    eq_word_define(dimen_base + display_indent_code, s);
    eq_word_define(int_base + pre_display_direction_code, (math_and_text_reversed_p() ? -1 : 0));
    if (every_display_par != null)
        begin_token_list(every_display_par, every_display_text);
    if (nest_ptr == 1) {
        checked_page_filter(before_display);
        build_page();
    }
}

/*tex

    The next routine parses all variations of a delimiter code. The |extcode|
    tells what syntax form to use (\TeX, XeTeX, XeTeXnum, ...) , the |doclass|
    tells whether or not read a math class also (for \.{\\delimiter} c.s.). (the
    class is passed on for conversion to \.{\\mathchar}).

*/

static delcodeval do_scan_extdef_del_code(int extcode, boolean doclass)
{
    const char *hlp[] = {
        "I'm going to use 0 instead of that illegal code value.",
        NULL
    };
    delcodeval d;
    int mcls = 0, msfam = 0, mschr = 0, mlfam = 0, mlchr = 0;
    if (extcode == tex_mathcode) {
        /*tex

            \.{\\delcode}, this is the easiest

        */
        scan_int();
        /*tex  "MFCCFCC or "FCCFCC */
        if (doclass) {
            mcls = (cur_val / 0x1000000);
            cur_val = (cur_val & 0xFFFFFF);
        }
        if (cur_val > 0xFFFFFF) {
            tex_error("Invalid delimiter code", hlp);
            cur_val = 0;
        }
        msfam = (cur_val / 0x100000);
        mschr = (cur_val % 0x100000) / 0x1000;
        mlfam = (cur_val & 0xFFF) / 0x100;
        mlchr = (cur_val % 0x100);
    } else if (extcode == umath_mathcode) {
        /*tex

            \.{\\Udelcode}: <0-7>,<0-0xFF>,<0-0x10FFFF>  or <0-0xFF>,<0-0x10FFFF>

        */
        if (doclass) {
            scan_int();
            mcls = cur_val;
        }
        scan_int();
        msfam = cur_val;
        scan_char_num();
        mschr = cur_val;
        if (msfam < 0 || msfam > 255) {
            tex_error("Invalid delimiter code", hlp);
            msfam = 0;
            mschr = 0;
        }
        mlfam = 0;
        mlchr = 0;
    } else if (extcode == umathnum_mathcode) {
        /*tex

           \.{\\Udelcodenum}:"FF<21bits>; the largest numeric value is $2^29-1$,
           but the top of bit 21 can't be used as it contains invalid USV's.

        */
        if (doclass) {          /* such a primitive doesn't exist */
            confusion("umathnum_mathcode");
        }
        scan_int();
        msfam = (cur_val / 0x200000);
        mschr = cur_val & 0x1FFFFF;
        if (msfam < 0 || msfam > 255 || mschr > 0x10FFFF) {
            tex_error("Invalid delimiter code", hlp);
            msfam = 0;
            mschr = 0;
        }
        mlfam = 0;
        mlchr = 0;
    } else {
        /*tex Something's gone wrong! */
        confusion("unknown_extcode");
    }
    d.class_value = mcls;
    d.small_family_value = msfam;
    d.small_character_value = mschr;
    d.large_family_value = mlfam;
    d.large_character_value = mlchr;
    return d;
}

void scan_extdef_del_code(int level, int extcode)
{
    delcodeval d;
    int p;
    scan_char_num();
    p = cur_val;
    scan_optional_equals();
    d = do_scan_extdef_del_code(extcode, false);
    set_del_code(p, d.small_family_value, d.small_character_value,
        d.large_family_value, d.large_character_value, (quarterword) (level));
}

mathcodeval scan_mathchar(int extcode)
{
    char errstr[255] = { 0 };
    const char *hlp[] = {
        "I'm going to use 0 instead of that illegal code value.",
        NULL
    };
    mathcodeval d;
    int mcls = 0, mfam = 0, mchr = 0;
    if (extcode == tex_mathcode) {
        /*tex \.{\\mathcode}: "TFCC */
        scan_int();
        if (cur_val > 0x8000) {
            /*tex Needed for latex: fallback to umathnum_mathcode. */
            mfam = (cur_val / 0x200000) & 0x7FF;
            mcls = mfam % 0x08;
            mfam = mfam / 0x08;
            mchr = cur_val & 0x1FFFFF;
            if (mchr > 0x10FFFF) {
                tex_error("Invalid math code during > 0x8000 mathcode fallback", hlp);
                mcls = 0;
                mfam = 0;
                mchr = 0;
            }
        } else {
            if (cur_val < 0) {
                snprintf(errstr, 255, "Bad mathchar (%d)", (int)cur_val);
                tex_error(errstr, hlp);
                cur_val = 0;
            }
            mcls = (cur_val / 0x1000);
            mfam = ((cur_val % 0x1000) / 0x100);
            mchr = (cur_val % 0x100);
        }
    } else if (extcode == umath_mathcode) {
        /*tex <0-0x7> <0-0xFF> <0-0x10FFFF> */
        scan_int();
        mcls = cur_val;
        scan_int();
        mfam = cur_val;
        scan_char_num();
        mchr = cur_val;
        if (mcls < 0 || mcls > 7 || mfam > 255) {
            tex_error("Invalid math code", hlp);
            mchr = 0;
            mfam = 0;
            mcls = 0;
        }
    } else if (extcode == umathnum_mathcode) {
        /*tex

            "FFT<21bits>: the largest numeric value is $2^32-1$, but the top of
            bit 21 can't be used as it contains invalid USV's

            Note: |scan_int| won't accept families 128-255 because these use bit 32

        */
        scan_int();
        mfam = (cur_val / 0x200000) & 0x7FF;
        mcls = mfam % 0x08;
        mfam = mfam / 0x08;
        mchr = cur_val & 0x1FFFFF;
        if (mchr > 0x10FFFF) {
            tex_error("Invalid math code", hlp);
            mcls = 0;
            mfam = 0;
            mchr = 0;
        }
    } else {
        /*tex Something's gone wrong. */
        confusion("unknown_extcode");
    }
    d.class_value = mcls;
    d.family_value = mfam;
    d.character_value = mchr;
    return d;
}

void scan_extdef_math_code(int level, int extcode)
{
    mathcodeval d;
    int p;
    scan_char_num();
    p = cur_val;
    scan_optional_equals();
    d = scan_mathchar(extcode);
    set_math_code(p, d.class_value, d.family_value, d.character_value, (quarterword) (level));
}

/*tex This reads in a delcode when actually a mathcode is needed. */

mathcodeval scan_delimiter_as_mathchar(int extcode)
{
    delcodeval dval;
    mathcodeval mval;
    dval = do_scan_extdef_del_code(extcode, true);
    mval.class_value = dval.class_value;
    mval.family_value = dval.small_family_value;
    mval.character_value = dval.small_character_value;
    return mval;
}

/*tex

    Recall that the |nucleus|, |subscr|, and |supscr| fields in a noad are broken
    down into subfields called |type| and either |math_list| or
    |(math_fam,math_character)|. The job of |scan_math| is to figure out what to
    place in one of these principal fields; it looks at the subformula that comes
    next in the input, and places an encoding of that subformula into a given
    word of |mem|.

*/

#define get_next_nb_nr() do { get_x_token(); } while (cur_cmd==spacer_cmd||cur_cmd==relax_cmd)

int scan_math_style(pointer p, int mstyle)
{
    get_next_nb_nr();
    back_input();
    scan_left_brace();
    set_saved_record(0, saved_math, 0, p);
    incr(save_ptr);
    push_math(math_group, mstyle);
    return 1;
}

int scan_math(pointer p, int mstyle)
{
    mathcodeval mval = { 0, 0, 0 };
    assert(p != null);
  RESTART:
    get_next_nb_nr();
  RESWITCH:
    switch (cur_cmd) {
    case letter_cmd:
    case other_char_cmd:
    case char_given_cmd:
        mval = get_math_code(cur_chr);
        if (mval.class_value == 8) {
            /*tex An active character that is an |outer_call| is allowed here. */
            cur_cs = active_to_cs(cur_chr, true);
            cur_cmd = eq_type(cur_cs);
            cur_chr = equiv(cur_cs);
            x_token();
            back_input();
            goto RESTART;
        }
        break;
    case char_num_cmd:
        scan_char_num();
        cur_chr = cur_val;
        cur_cmd = char_given_cmd;
        goto RESWITCH;
        break;
    case math_char_num_cmd:
        if (cur_chr == 0)
            mval = scan_mathchar(tex_mathcode);
        else if (cur_chr == 1)
            mval = scan_mathchar(umath_mathcode);
        else if (cur_chr == 2)
            mval = scan_mathchar(umathnum_mathcode);
        else
            confusion("scan_math");
        break;
    case math_given_cmd:
        mval = mathchar_from_integer(cur_chr, tex_mathcode);
        break;
    case xmath_given_cmd:
        mval = mathchar_from_integer(cur_chr, umath_mathcode);
        break;
    case delim_num_cmd:
        if (cur_chr == 0)
            mval = scan_delimiter_as_mathchar(tex_mathcode);
        else if (cur_chr == 1)
            mval = scan_delimiter_as_mathchar(umath_mathcode);
        else
            confusion("scan_math");
        break;
    default:
        /*tex

            The pointer |p| is placed on |save_stack| while a complex subformula
            is being scanned.

        */
        back_input();
        scan_left_brace();
        set_saved_record(0, saved_math, 0, p);
        incr(save_ptr);
        push_math(math_group, mstyle);
        return 1;
    }
    type(p) = math_char_node;
    math_character(p) = mval.character_value;
    if ((mval.class_value == math_use_current_family_code) && cur_fam_par_in_range)
        math_fam(p) = cur_fam_par;
    else
        math_fam(p) = mval.family_value;
    return 0;
}

/*tex

    The |set_math_char| procedure creates a new noad appropriate to a given math
    code, and appends it to the current mlist. However, if the math code is
    sufficiently large, the |cur_chr| is treated as an active character and
    nothing is appended.

*/

#define math_class_to_type(target,source) \
    switch (source) { \
        case 0: target = ord_noad_type; break; \
        case 1: target = op_noad_type_normal; break; \
        case 2: target = bin_noad_type; break; \
        case 3: target = rel_noad_type; break; \
        case 4: target = open_noad_type; break; \
        case 5: target = close_noad_type; break; \
        case 6: target = punct_noad_type; break; \
    }

void set_math_char(mathcodeval mval)
{
    pointer p;
    if (mval.class_value == 8) {
        /*tex An active character that is an |outer_call| is allowed here */
        cur_cs = active_to_cs(cur_chr, true);
        cur_cmd = eq_type(cur_cs);
        cur_chr = equiv(cur_cs);
        x_token();
        back_input();
    } else {
        pointer q;
        p = new_noad();
        q = new_node(math_char_node, 0);
        nucleus(p) = q;
        math_character(nucleus(p)) = mval.character_value;
        math_fam(nucleus(p)) = mval.family_value;
        if (mval.class_value == math_use_current_family_code) {
            if (cur_fam_par_in_range)
                math_fam(nucleus(p)) = cur_fam_par;
            subtype(p) = ord_noad_type;
        } else {
            math_class_to_type(subtype(p),mval.class_value);
        }
        tail_append(p);
    }
}

/*tex

    The |math_char_in_text| procedure creates a new node representing a math char
    in text code, and appends it to the current list. However, if the math code
    is sufficiently large, the |cur_chr| is treated as an active character and
    nothing is appended.

*/

void math_char_in_text(mathcodeval mval)
{
    pointer p;
    if (mval.class_value == 8) {
        /*tex An active character that is an |outer_call| is allowed here */
        cur_cs = active_to_cs(cur_chr, true);
        cur_cmd = eq_type(cur_cs);
        cur_chr = equiv(cur_cs);
        x_token();
        back_input();
    } else {
        p = new_char(fam_fnt(mval.family_value, text_size), mval.character_value);
        tail_append(p);
    }
}

void math_math_comp(void)
{
    pointer q;
    tail_append(new_noad());
    subtype(tail) = (quarterword) cur_chr;
    q = new_node(math_char_node, 0);
    nucleus(tail) = q;
    if (cur_chr == over_noad_type)
        (void) scan_math(nucleus(tail), cramped_style(m_style));
    else
        (void) scan_math(nucleus(tail), m_style);
}

void math_limit_switch(void)
{
    const char *hlp[] = {
        "I'm ignoring this misplaced \\limits or \\nolimits command.",
        NULL
    };
    if (head != tail) {
         if (type(tail) == simple_noad &&
             (subtype(tail) == op_noad_type_normal ||
              subtype(tail) == op_noad_type_limits ||
              subtype(tail) == op_noad_type_no_limits)) {
            subtype(tail) = (quarterword) cur_chr;
            return;
        }
    }
    tex_error("Limit controls must follow a math operator", hlp);
}

/*tex

     Delimiter fields of noads are filled in by the |scan_delimiter| routine. The
     first parameter of this procedure is the |mem| address where the delimiter
     is to be placed; the second tells if this delimiter follows \.{\\radical} or
     not.

*/

static void scan_delimiter(pointer p, int r)
{
    delcodeval dval = { 0, 0, 0, 0, 0 };
    if (r == tex_mathcode) {
        /*tex \.{\\radical} */
        dval = do_scan_extdef_del_code(tex_mathcode, true);
    } else if (r == umath_mathcode) {
        /*tex \.{\\Uradical} */
        dval = do_scan_extdef_del_code(umath_mathcode, false);
    } else if (r == no_mathcode) {
        get_next_nb_nr();
        switch (cur_cmd) {
        case letter_cmd:
        case other_char_cmd:
            dval = get_del_code(cur_chr);
            break;
        case delim_num_cmd:
            if (cur_chr == 0) {
                /*tex \.{\\delimiter} */
                dval = do_scan_extdef_del_code(tex_mathcode, true);
            } else if (cur_chr == 1) {
                /*tex \.{\\Udelimiter} */
                dval = do_scan_extdef_del_code(umath_mathcode, true);
            } else {
                confusion("scan_delimiter1");
            }
            break;
        default:
            dval.small_family_value = -1;
            break;
        }
    } else {
        confusion("scan_delimiter2");
    }
    if (p == null)
        return;
    if (dval.small_family_value < 0) {
        const char *hlp[] = {
            "I was expecting to see something like `(' or `\\{' or",
            "`\\}' here. If you typed, e.g., `{' instead of `\\{', you",
            "should probably delete the `{' by typing `1' now, so that",
            "braces don't get unbalanced. Otherwise just proceed",
            "Acceptable delimiters are characters whose \\delcode is",
            "nonnegative, or you can use `\\delimiter <delimiter code>'.",
            NULL
        };
        back_error("Missing delimiter (. inserted)", hlp);
        small_fam(p) = 0;
        small_char(p) = 0;
        large_fam(p) = 0;
        large_char(p) = 0;
    } else {
        small_fam(p) = dval.small_family_value;
        small_char(p) = dval.small_character_value;
        large_fam(p) = dval.large_family_value;
        large_char(p) = dval.large_character_value;
    }
    return;
}

void math_radical(void)
{
    halfword q;
    int chr_code = cur_chr;
    halfword options = 0;
    tail_append(new_node(radical_noad, chr_code));
    q = new_node(delim_node, 0);
    left_delimiter(tail) = q;
    while (1) {
        if (scan_keyword("width")) {
            scan_dimen(false,false,false);
            radicalwidth(tail) = cur_val ;
        } else if (scan_keyword("left")) {
            options = options | noad_option_left ;
        } else if (scan_keyword("middle")) {
            options = options | noad_option_middle ;
        } else if (scan_keyword("right")) {
            options = options | noad_option_right ;
        } else {
            break;
        }
    }
    radicaloptions(tail) = options;
    if (chr_code == 0)
        /*tex \.{\\radical} */
        scan_delimiter(left_delimiter(tail), tex_mathcode);
    else if (chr_code == 1)
        /*tex \.{\\Uradical} */
        scan_delimiter(left_delimiter(tail), umath_mathcode);
    else if (chr_code == 2)
        /*tex \.{\\Uroot} */
        scan_delimiter(left_delimiter(tail), umath_mathcode);
    else if (chr_code == 3)
        /*tex \.{\\Uunderdelimiter} */
        scan_delimiter(left_delimiter(tail), umath_mathcode);
    else if (chr_code == 4)
        /*tex \.{\\Uoverdelimiter} */
        scan_delimiter(left_delimiter(tail), umath_mathcode);
    else if (chr_code == 5)
        /*tex \.{\\Udelimiterunder} */
        scan_delimiter(left_delimiter(tail), umath_mathcode);
    else if (chr_code == 6)
        /*tex \.{\\Udelimiterover} */
        scan_delimiter(left_delimiter(tail), umath_mathcode);
    else if (chr_code == 7)
        /*tex \.{\\Uhextensible} */
        scan_delimiter(left_delimiter(tail), umath_mathcode);
    else
        confusion("math_radical");
    if (chr_code == 7) {
        /*tex type will change */
        q = new_node(sub_box_node, 0);
        nucleus(tail) = q;
        return;
    } else if (chr_code == 2) {
        /*tex

            The trick with the |vlink(q)| is used by |scan_math| to decide
            whether it needs to go on.

        */
        q = new_node(math_char_node, 0);
        vlink(q) = tail;
        degree(tail) = q;
        if (!scan_math(degree(tail), sup_sup_style(m_style))) {
            vlink(degree(tail)) = null;
            q = new_node(math_char_node, 0);
            nucleus(tail) = q;
            (void) scan_math(nucleus(tail), cramped_style(m_style));
        }
    } else {
        q = new_node(math_char_node, 0);
        nucleus(tail) = q;
        (void) scan_math(nucleus(tail), cramped_style(m_style));
    }
}

void math_ac(void)
{
    halfword q;
    mathcodeval t = { 0, 0, 0 };
    mathcodeval b = { 0, 0, 0 };
    mathcodeval o = { 0, 0, 0 };
    if (cur_cmd == accent_cmd) {
        const char *hlp[] = {
            "I'm changing \\accent to \\mathaccent here; wish me luck.",
            "(Accents are not the same in formulas as they are in text.)",
            NULL
        };
        tex_error("Please use \\mathaccent for accents in math mode", hlp);
    }
    tail_append(new_node(accent_noad, 0));
    if (cur_chr == 0) {
        /*tex \.{\\mathaccent} */
        t = scan_mathchar(tex_mathcode);
    } else if (cur_chr == 1) {
        /*tex \.{\\Umathaccent} */
        if (scan_keyword("fixed")) {
            /*tex top */
            subtype(tail) = 1;
            t = scan_mathchar(umath_mathcode);
        } else if (scan_keyword("both")) {
            /*tex top bottom */
            if (scan_keyword("fixed")) {
                subtype(tail) = 1;
            }
            t = scan_mathchar(umath_mathcode);
            if (scan_keyword("fixed")) {
                subtype(tail) += 2;
            }
            b = scan_mathchar(umath_mathcode);
        } else if (scan_keyword("bottom")) {
            /*tex bottom */
            if (scan_keyword("fixed")) {
                subtype(tail) = 2;
            }
            b = scan_mathchar(umath_mathcode);
        } else if (scan_keyword("top")) {
            /*tex top */
            if (scan_keyword("fixed")) {
                subtype(tail) = 1;
            }
            t = scan_mathchar(umath_mathcode);
        } else if (scan_keyword("overlay")) {
            /* overlay */
            if (scan_keyword("fixed")) {
                subtype(tail) = 1;
            }
            o = scan_mathchar(umath_mathcode);
        } else {
            /*tex top */
            t = scan_mathchar(umath_mathcode);
        }
        if (scan_keyword("fraction")) {
            scan_int();
            accentfraction(tail) = cur_val;
        }
    } else {
        confusion("mathaccent");
    }
    if (!(t.character_value == 0 && t.family_value == 0)) {
        q = new_node(math_char_node, 0);
        top_accent_chr(tail) = q;
        math_character(top_accent_chr(tail)) = t.character_value;
        if ((t.class_value == math_use_current_family_code) && cur_fam_par_in_range)
            math_fam(top_accent_chr(tail)) = cur_fam_par;
        else
            math_fam(top_accent_chr(tail)) = t.family_value;
    }
    if (!(b.character_value == 0 && b.family_value == 0)) {
        q = new_node(math_char_node, 0);
        bot_accent_chr(tail) = q;
        math_character(bot_accent_chr(tail)) = b.character_value;
        if ((b.class_value == math_use_current_family_code) && cur_fam_par_in_range)
            math_fam(bot_accent_chr(tail)) = cur_fam_par;
        else
            math_fam(bot_accent_chr(tail)) = b.family_value;
    }
    if (!(o.character_value == 0 && o.family_value == 0)) {
        q = new_node(math_char_node, 0);
        overlay_accent_chr(tail) = q;
        math_character(overlay_accent_chr(tail)) = o.character_value;
        if ((o.class_value == math_use_current_family_code) && cur_fam_par_in_range)
            math_fam(overlay_accent_chr(tail)) = cur_fam_par;
        else
            math_fam(overlay_accent_chr(tail)) = o.family_value;
    }
    q = new_node(math_char_node, 0);
    nucleus(tail) = q;
    (void) scan_math(nucleus(tail), cramped_style(m_style));
}

pointer math_vcenter_group(pointer p)
{
    pointer q, r;
    q = new_noad();
    subtype(q) = vcenter_noad_type;
    r = new_node(sub_box_node, 0);
    nucleus(q) = r;
    math_list(nucleus(q)) = p;
    return q;
}

/*tex

    The routine that scans the four mlists of a \.{\\mathchoice} is very much
    like the routine that builds discretionary nodes.

*/

void append_choices(void)
{
    tail_append(new_choice());
    incr(save_ptr);
    set_saved_record(-1, saved_choices, 0, 0);
    push_math(math_choice_group, display_style);
    scan_left_brace();
}

void build_choices(void)
{
    pointer p;
    int prev_style;
    prev_style = m_style;
    unsave_math();
    p = fin_mlist(null);
    assert(saved_type(-1) == saved_choices);
    switch (saved_value(-1)) {
    case 0:
        display_mlist(tail) = p;
        break;
    case 1:
        text_mlist(tail) = p;
        break;
    case 2:
        script_mlist(tail) = p;
        break;
    case 3:
        script_script_mlist(tail) = p;
        decr(save_ptr);
        return;
        break;
    }
    set_saved_record(-1, saved_choices, 0, (saved_value(-1) + 1));
    push_math(math_choice_group, (prev_style + 2));
    scan_left_brace();
}

/*tex

    Subscripts and superscripts are attached to the previous nucleus by the
    action procedure called |sub_sup|.

*/

static void do_sub_sup(int no)
{
    pointer q;
    if (tail == head || (!scripts_allowed(tail))) {
        tail_append(new_noad());
        q = new_node(sub_mlist_node, 0);
        nucleus(tail) = q;
    }
    if (cur_cmd == sup_mark_cmd || cur_chr == sup_mark_cmd) {
        /*tex |super_sub_script| */
        if (supscr(tail) != null) {
            const char *hlp[] = {
                "I treat `x^1^2' essentially like `x^1{}^2'.", NULL
            };
            tail_append(new_noad());
            q = new_node(sub_mlist_node, 0);
            nucleus(tail) = q;
            tex_error("Double superscript", hlp);
        }
        if (no) {
            noadoptions(tail) = noadoptions(tail) | noad_option_no_super_script ;
        }
        q = new_node(math_char_node, 0);
        supscr(tail) = q;
        (void) scan_math(supscr(tail), sup_style(m_style));
    } else if (cur_cmd == sub_mark_cmd || cur_chr == sub_mark_cmd) {
        if (subscr(tail) != null) {
            const char *hlp[] = {
                "I treat `x_1_2' essentially like `x_1{}_2'.", NULL
            };
            tail_append(new_noad());
            q = new_node(sub_mlist_node, 0);
            nucleus(tail) = q;
            tex_error("Double subscript", hlp);
        }
        if (no) {
            noadoptions(tail) = noadoptions(tail) | noad_option_no_sub_script ;
        }
        q = new_node(math_char_node, 0);
        subscr(tail) = q;
        (void) scan_math(subscr(tail), sub_style(m_style));
    }
}

void sub_sup(void)
{
    do_sub_sup(0);
}

void no_sub_sup(void)
{
    do_sub_sup(1);
}

/*tex

    An operation like `\.{\\over}' causes the current mlist to go into a state of
    suspended animation: |incompleat_noad| points to a |fraction_noad| that
    contains the mlist-so-far as its numerator, while the denominator is yet to
    come. Finally when the mlist is finished, the denominator will go into the
    incompleat fraction noad, and that noad will become the whole formula, unless
    it is surrounded by `\.{\\left}' and `\.{\\right}' delimiters.

*/

void math_fraction(void)
{
    /*tex The type of generalized fraction we are scanning: */
    halfword c;
    pointer q;
    halfword options = 0;
    halfword temp_value;
    c = cur_chr;
    if (incompleat_noad_par != null) {
        const char *hlp[] = {
            "I'm ignoring this fraction specification, since I don't",
            "know whether a construction like `x \\over y \\over z'",
            "means `{x \\over y} \\over z' or `x \\over {y \\over z}'.",
            NULL
        };
        if (c >= delimited_code) {
            scan_delimiter(null, no_mathcode);
            scan_delimiter(null, no_mathcode);
        }
        if ((c % delimited_code) == above_code)
            scan_normal_dimen();
        tex_error("Ambiguous; you need another { and }", hlp);
    } else {
        incompleat_noad_par = new_node(fraction_noad, 0);
        temp_value = new_node(sub_mlist_node, 0);
        numerator(incompleat_noad_par) = temp_value;
        math_list(numerator(incompleat_noad_par)) = vlink(head);
        vlink(head) = null;
        tail = head;
        m_style = cramped_style(m_style);

        if ((c % delimited_code) == skewed_code) {
            q = new_node(delim_node, 0);
            middle_delimiter(incompleat_noad_par) = q;
            scan_delimiter(middle_delimiter(incompleat_noad_par), no_mathcode);
        }
        if (c >= delimited_code) {
            q = new_node(delim_node, 0);
            left_delimiter(incompleat_noad_par) = q;
            q = new_node(delim_node, 0);
            right_delimiter(incompleat_noad_par) = q;
            scan_delimiter(left_delimiter(incompleat_noad_par), no_mathcode);
            scan_delimiter(right_delimiter(incompleat_noad_par), no_mathcode);
        }
        switch (c % delimited_code) {
            case above_code:
                while (1) {
                    if (scan_keyword("exact")) {
                        options = options | noad_option_exact ;
                    } else if (scan_keyword("norule")) {
                        options = options | noad_option_no_rule ;
                    } else {
                        break;
                    }
                }
                fractionoptions(incompleat_noad_par) = options;
                scan_normal_dimen();
                thickness(incompleat_noad_par) = cur_val;
                break;
            case over_code:
                thickness(incompleat_noad_par) = default_code;
                break;
            case atop_code:
                thickness(incompleat_noad_par) = 0;
                break;
            case skewed_code:
                while (1) {
                    if (scan_keyword("exact")) {
                        options = options | noad_option_exact ;
                    } else if (scan_keyword("noaxis")) {
                        options = options | noad_option_no_axis ;
                    } else {
                        break;
                    }
                }
                fractionoptions(incompleat_noad_par) = options;
                thickness(incompleat_noad_par) = 0;
                break;
        }
    }
}

/*tex

    At the end of a math formula or subformula, the |fin_mlist| routine is called
    upon to return a pointer to the newly completed mlist, and to pop the nest
    back to the enclosing semantic level. The parameter to |fin_mlist|, if not
    null, points to a |fence_noad| that ends the current mlist; this |fence_noad|
    has not yet been appended.

*/

pointer fin_mlist(pointer p)
{
    pointer q;
    if (incompleat_noad_par != null) {
        if (denominator(incompleat_noad_par) != null) {
            type(denominator(incompleat_noad_par)) = sub_mlist_node;
        } else {
            q = new_node(sub_mlist_node, 0);
            denominator(incompleat_noad_par) = q;
        }
        math_list(denominator(incompleat_noad_par)) = vlink(head);
        if (p == null) {
            q = incompleat_noad_par;
        } else {
            q = math_list(numerator(incompleat_noad_par));
            if ((type(q) != fence_noad) || (subtype(q) != left_noad_side) || (delim_par == null))
                confusion("right");
            math_list(numerator(incompleat_noad_par)) = vlink(delim_par);
            vlink(delim_par) = incompleat_noad_par;
            vlink(incompleat_noad_par) = p;
        }
    } else {
        vlink(tail) = p;
        q = vlink(head);
    }
    pop_nest();
    return q;
}

/*tex

    Now at last we're ready to see what happens when a right brace occurs in a
    math formula. Two special cases are simplified here: Braces are effectively
    removed when they surround a single Ord without sub/superscripts, or when
    they surround an accent that is the nucleus of an Ord atom.

*/

void close_math_group(pointer p)
{
    int old_style = m_style;
    unsave_math();
    decr(save_ptr);
    assert(saved_type(0) == saved_math);
    type(saved_value(0)) = sub_mlist_node;
    p = fin_mlist(null);
    math_list(saved_value(0)) = p;
    if (p != null && vlink(p) == null) {
        if (type(p) == simple_noad) {
            if (subscr(p) == null && supscr(p) == null) {
                /*tex (subtype(p) == ord_noad_type) */
                int flatten = 0;
                int modepar = math_flatten_mode_par;
                switch (subtype(p)) {
                    case ord_noad_type :
                        flatten = (modepar & 1) == 1;
                        break;
                    case bin_noad_type :
                        flatten = (modepar & 2) == 2;
                        break;
                    case rel_noad_type :
                        flatten = (modepar & 4) == 4;
                        break;
                    case punct_noad_type :
                        flatten = (modepar & 8) == 8;
                        break;
                    case inner_noad_type :
                        flatten = (modepar & 16) == 16;
                        break;
                    default:
                        break;
                }
                if (flatten) {
                    type(saved_value(0)) = type(nucleus(p));
                    if (type(nucleus(p)) == math_char_node) {
                        math_fam(saved_value(0)) = math_fam(nucleus(p));
                        math_character(saved_value(0)) =
                            math_character(nucleus(p));
                    } else {
                        math_list(saved_value(0)) = math_list(nucleus(p));
                        math_list(nucleus(p)) = null;
                    }
                    delete_attribute_ref(node_attr(saved_value(0)));
                    node_attr(saved_value(0)) = node_attr(nucleus(p));
                    node_attr(nucleus(p)) = null;
                    flush_node(p);
                }
            }
        } else if (type(p) == accent_noad) {
            if (saved_value(0) == nucleus(tail) && type(tail) == simple_noad  && subtype(tail) == ord_noad_type) {
                pointer q = head;
                while (vlink(q) != tail)
                    q = vlink(q);
                vlink(q) = p;
                nucleus(tail) = null;
                subscr(tail) = null;
                supscr(tail) = null;
                delete_attribute_ref(node_attr(p));
                node_attr(p) = node_attr(tail);
                node_attr(tail) = null;
                flush_node(tail);
                tail = p;
            }
        }
    }
    if (vlink(saved_value(0)) > 0) {
        pointer q;
        q = new_node(math_char_node, 0);
        nucleus(vlink(saved_value(0))) = q;
        vlink(saved_value(0)) = null;
        saved_value(0) = q;
        (void) scan_math(saved_value(0), old_style);
        /*tex restart */
    }
}

/*tex

    We have dealt with all constructions of math mode except `\.{\\left}' and
    `\.{\\right}', so the picture is completed by the following sections of the
    program. The |middle| feature of eTeX allows one ore several \.{\\middle}
    delimiters to appear between \.{\\left} and \.{\\right}.

*/

void math_left_right(void)
{
    /*tex |left_noad_side| .. |right_noad_side| */
    halfword t;
    /*tex new noad */
    pointer p;
    /*tex resulting mlist */
    pointer q;
    /*tex temporary */
    pointer r;
    halfword ht = 0;
    halfword dp = 0;
    halfword options = 0;
    halfword type = -1 ;
    t = cur_chr;
    if (t > 10) {
        /*tex we have \Uleft \Uright \Umiddle */
        t = t - 10;
        while (1) {
            if (scan_keyword("height")) {
                scan_dimen(false,false,false);
                ht = cur_val ;
            } else if (scan_keyword("depth")) {
                scan_dimen(false,false,false);
                dp = cur_val ;
            } else if (scan_keyword("axis")) {
                options = options | noad_option_axis ;
            } else if (scan_keyword("noaxis")) {
                options = options | noad_option_no_axis ;
            } else if (scan_keyword("exact")) {
                options = options | noad_option_exact ;
            } else if (scan_keyword("class")) {
                scan_int();
                math_class_to_type(type,cur_val);
            } else {
                break;
            }
        }
    }
    if ((t != no_noad_side) && (t != left_noad_side) && (cur_group != math_left_group)) {
        if (cur_group == math_shift_group) {
            scan_delimiter(null, no_mathcode);
            if (t == middle_noad_side) {
                const char *hlp[] = {
                    "I'm ignoring a \\middle that had no matching \\left.",
                    NULL
                };
                tex_error("Extra \\middle", hlp);
            } else {
                const char *hlp[] = {
                    "I'm ignoring a \\right that had no matching \\left.",
                    NULL
                };
                tex_error("Extra \\right", hlp);
            }
        } else {
            off_save();
        }
    } else {
        p = new_noad();
        type(p) = fence_noad;
        subtype(p) = (quarterword) t;
        r = new_node(delim_node, 0);
        delimiter(p) = r;
        delimiterheight(p) = ht;
        delimiterdepth(p) = dp;
        delimiteroptions(p) = options;
        delimiterclass(p) = type;
        delimiteritalic(p) = 0;
        delimitersamesize(p) = 0;
        scan_delimiter(delimiter(p), no_mathcode);
        if (t == no_noad_side) {
            tail_append(new_noad());
            subtype(tail) = inner_noad_type;
            r = new_node(sub_mlist_node, 0);
            nucleus(tail) = r;
            math_list(nucleus(tail)) = p;
            return ;
        }
        if (t == left_noad_side) {
            q = p;
        } else {
            q = fin_mlist(p);
            unsave_math();
        }
        if (t != right_noad_side) {
            push_math(math_left_group, m_style);
            vlink(head) = q;
            tail = p;
            delim_par = p;
        } else {
            tail_append(new_noad());
            subtype(tail) = inner_noad_type;
            r = new_node(sub_mlist_node, 0);
            nucleus(tail) = r;
            math_list(nucleus(tail)) = q;
        }
    }
}

/*tex

    \TeX\ gets to the following part of the program when the first `\.\$' ending
    a display has been scanned.

*/

static void check_second_math_shift(void)
{
    get_x_token();
    if (cur_cmd != math_shift_cmd) {
        const char *hlp[] = {
            "The `$' that I just saw supposedly matches a previous `$$'.",
            "So I shall assume that you typed `$$' both times.",
            NULL
        };
        back_error("Display math should end with $$", hlp);
    }
}

static void check_display_math_end(void)
{
    if (cur_chr != cramped_display_style) {
        const char *hlp[] = {
            "I shall assume that you typed that.",
            NULL
        };
        tex_error("Display math should end with \\Ustopdisplaymath", hlp);
    }
}

static void check_inline_math_end(void)
{
    if (cur_chr != cramped_text_style) {
        const char *hlp[] = {
            "I shall assume that you typed that.",
            NULL
        };
        tex_error("Inline math should end with \\Ustopmath", hlp);
    }
}

static void resume_after_display(void)
{
    if (cur_group != math_shift_group)
        confusion("display");
    unsave_math();
    prev_graf_par = prev_graf_par + 3;
    push_nest();
    mode = hmode;
    space_factor_par = 1000;
    /*tex This needs to be intercepted in the display math start! */
    tail_append(make_local_par_node(penalty_par_code));
    get_x_token();
    if (cur_cmd != spacer_cmd)
        back_input();
    if (nest_ptr == 1) {
        normal_page_filter(after_display);
        build_page();
    }
}

/*tex

    The fussiest part of math mode processing occurs when a displayed formula is
    being centered and placed with an optional equation number.

    At this time we are in vertical mode (or internal vertical mode).

    \starttabulate
    \NC \type {p} \NC points to the mlist for the formula \NC \NR
    \NC \type {a} \NC is either |null| or it points to a box containing the equation number \NC \NR
    \NC \type {l} \NC is true if there was an \.{\\leqno}/ (so |a| is a horizontal box) \NC \NR
    \stoptabulate

*/

#define inject_display_skip_before(g) \
    if (g > 0) { \
        switch (display_skip_mode_par) { \
            case 0 : \
                /*tex normal tex | always */ \
            case 1 : \
                /*tex always */ \
                tail_append(new_param_glue(g)); \
                break; \
            case 2 : \
                /*tex non-zero */ \
                if (! glue_is_zero(glue_par(g))) \
                    tail_append(new_param_glue(g)); \
                break; \
            case 3: \
                /*tex ignore */ \
                break; \
            default: \
                /*tex > 3 reserved for future use */ \
                tail_append(new_param_glue(g)); \
                break; \
        } \
    }

#define inject_display_skip_after(g) \
    if (g > 0) { \
        switch (display_skip_mode_par) { \
            case 0 : \
                /*tex normal tex | always */ \
            case 1 : \
                /*tex always */ \
                tail_append(new_param_glue(g)); \
                break; \
            case 2 : \
                /*tex non-zero */ \
                if (! glue_is_zero(glue_par(g))) \
                    tail_append(new_param_glue(g)); \
                break; \
            case 3: \
                /*tex ignore */ \
                break; \
            default: \
                /*tex > 3 reserved for future use */ \
                tail_append(new_param_glue(g)); \
                break; \
        } \
    }

static void finish_displayed_math(boolean l, pointer eqno_box, pointer p)
{
    /*tex box containing the equation */
    pointer eq_box;
    /*tex width of the equation */
    scaled eq_w;
    /*tex width of the line */
    scaled line_w;
    /*tex width of equation number */
    scaled eqno_w;
    /*tex width of equation number plus space to separate from equation */
    scaled eqno_w2;
    /*tex move the line right this much */
    scaled line_s;
    /*tex displacement of equation in the line */
    scaled d;
    /*tex glue parameter codes for before and after */
    small_number g1, g2;
    /*tex kern nodes used to position the display */
    pointer r,s;
    /*tex tail of adjustment list */
    pointer t;
    /*tex tail of pre-adjustment list */
    pointer pre_t;
    /*tex true if the math and surrounding text dirs are opposed */
    boolean swap_dir;
    scaled eqno_width;
    swap_dir = (pre_display_direction_par < 0 ? true : false );
    if (eqno_box != null && swap_dir)
        l = !l;
    adjust_tail = adjust_head;
    pre_adjust_tail = pre_adjust_head;
    eq_box = hpack(p, 0, additional, -1);
    subtype(eq_box) = equation_list;
    build_attribute_list(eq_box);
    p = list_ptr(eq_box);
    t = adjust_tail;
    adjust_tail = null;
    pre_t = pre_adjust_tail;
    pre_adjust_tail = null;
    eq_w = width(eq_box);
    line_w = display_width_par;
    line_s = display_indent_par;
    if (eqno_box == null) {
        eqno_w = 0;
        eqno_width = 0;
        eqno_w2 = 0;
    } else {
        eqno_w = width(eqno_box);
        eqno_width = eqno_w;
        eqno_w2 = eqno_w + round_xn_over_d(math_eqno_gap_step_par, get_math_quad_style(text_style), 1000);
        subtype(eqno_box) = equation_number_list;
        /*tex build_attribute_list(eqno_box); */
    }
    if (eq_w + eqno_w2 > line_w) {
        /*tex

            The user can force the equation number to go on a separate line by
            causing its width to be zero.

        */
        if ((eqno_w != 0) && ((eq_w - total_shrink[normal] + eqno_w2 <= line_w)
                || (total_shrink[sfi] != 0) || (total_shrink[fil] != 0)
                || (total_shrink[fill] != 0) || (total_shrink[filll] != 0))) {
            list_ptr(eq_box) = null;
            flush_node(eq_box);
            eq_box = hpack(p, line_w - eqno_w2, exactly, -1);
            subtype(eq_box) = equation_list;
            build_attribute_list(eq_box);
        } else {
            eqno_w = 0;
            if (eq_w > line_w) {
                list_ptr(eq_box) = null;
                flush_node(eq_box);
                eq_box = hpack(p, line_w, exactly, -1);
                subtype(eq_box) = equation_list;
                build_attribute_list(eq_box);
            }
        }
        eq_w = width(eq_box);
    }
    /*tex

        We try first to center the display without regard to the existence of the
        equation number. If that would make it too close (where ``too close''
        means that the space between display and equation number is less than the
        width of the equation number), we either center it in the remaining space
        or move it as far from the equation number as possible. The latter
        alternative is taken only if the display begins with glue, since we
        assume that the user put glue there to control the spacing precisely.

    */
    d = half(line_w - eq_w);
    if ((eqno_w > 0) && (d < 2 * eqno_w)) {
        /*tex too close */
        d = half(line_w - eq_w - eqno_w);
        if (p != null)
            if (!is_char_node(p))
                if (type(p) == glue_node)
                    d = 0;
    }
    tail_append(new_penalty(pre_display_penalty_par,after_display_penalty));
    if ((d + line_s <= pre_display_size_par) || l) {
        /*tex not enough clearance */
        g1 = above_display_skip_code;
        g2 = below_display_skip_code;
    } else {
        g1 = above_display_short_skip_code;
        g2 = below_display_short_skip_code;
    }
    /*tex

        If the equation number is set on a line by itself, either before or after
        the formula, we append an infinite penalty so that no page break will
        separate the display from its number; and we use the same size and
        displacement for all three potential lines of the display, even though
        `\.{\\parshape}' may specify them differently.

        \.{\\leqno} on a forced single line due to |width=0|; it follows that |type(a)=hlist_node|

    */
    if (eqno_box && l && (eqno_w == 0)) {
     /* if (math_direction_par==dir_TLT) { */
            shift_amount(eqno_box) = 0;
     /* } else {                       */
     /* }                              */
        append_to_vlist(eqno_box,lua_key_index(equation_number));
        tail_append(new_penalty(inf_penalty,equation_number_penalty));
    } else {
        inject_display_skip_before(g1);
    }
    if (eqno_w != 0) {
        r = new_kern(line_w - eq_w - eqno_w - d);
        if (l) {
            if (swap_dir) {
                if (math_direction_par==dir_TLT) {
                    /*tex TRT + TLT + \eqno: (swap_dir=true,  math_direction_par=TLT, l=true) */
                    s = new_kern(width(r) + eqno_w);
                    try_couple_nodes(eqno_box,r);
                    try_couple_nodes(r,eq_box);
                    try_couple_nodes(eq_box,s);
                } else {
                    /*tex TLT + TRT + \eqno: (swap_dir=true,  math_direction_par=TRT, l=true) */
                    try_couple_nodes(eqno_box,r);
                    try_couple_nodes(r,eq_box);
                }
            } else {
                if (math_direction_par==dir_TLT) {
                    /*tex TLT + TLT + \leqno: (swap_dir=false, math_direction_par=TLT, l=true) */
                    s = new_kern(width(r) + eqno_w);
                } else {
                    /*tex TRT + TRT + \leqno: (swap_dir=false, math_direction_par=TRT, l=true) */
                    s = new_kern(width(r));
                }
                try_couple_nodes(eqno_box,r);
                try_couple_nodes(r,eq_box);
                try_couple_nodes(eq_box,s);
            }
            eq_box = eqno_box;
        } else {
            if (swap_dir) {
                if (math_direction_par==dir_TLT) {
                    /*tex TRT + TLT + \leqno: (swap_dir=true,  math_direction_par=TLT, l=false) */
                } else {
                    /*tex TLT + TRT + \leqno: (swap_dir=true,  math_direction_par=TRT, l=false) */
                }
                try_couple_nodes(eq_box,r);
                try_couple_nodes(r,eqno_box);
            } else {
                if (math_direction_par==dir_TLT) {
                    /*tex TLT + TLT + \eqno: (swap_dir=false, math_direction_par=TLT, l=false) */
                    s = new_kern(d);
                } else {
                    /*tex TRT + TRT + \eqno: (swap_dir=false, math_direction_par=TRT, l=false) */
                    s = new_kern(width(r) + eqno_w);
                }
                try_couple_nodes(s,eq_box);
                try_couple_nodes(eq_box,r);
                try_couple_nodes(r,eqno_box);
                eq_box = s;
            }
        }
        eq_box = hpack(eq_box, 0, additional, -1);
        subtype(eq_box) = equation_list; /* new */
        build_attribute_list(eq_box);
        shift_amount(eq_box) = line_s;
    } else {
        shift_amount(eq_box) = line_s + d;
    }
    /*tex check for prev: */
    append_to_vlist(eq_box,lua_key_index(equation));
    if ((eqno_box != null) && (eqno_w == 0) && !l) {
        tail_append(new_penalty(inf_penalty,equation_number_penalty));
     /* if (math_direction_par==dir_TLT) { */
            shift_amount(eqno_box) = line_s + line_w - eqno_width ;
     /* } else {                       */
     /* }                              */
        append_to_vlist(eqno_box,lua_key_index(equation_number));
        g2 = 0;
    }
    if (t != adjust_head) {
        /*tex migrating material comes after equation number */
        vlink(tail) = vlink(adjust_head);
        alink(adjust_tail) = alink(tail);
        tail = t;
    }
    if (pre_t != pre_adjust_head) {
        vlink(tail) = vlink(pre_adjust_head);
        alink(pre_adjust_tail) = alink(tail);
        tail = pre_t;
    }
    tail_append(new_penalty(post_display_penalty_par,after_display_penalty));
    inject_display_skip_after(g2);
    resume_after_display();
}

void after_math(void)
{
    /*tex |mmode| or |-mmode| */
    int m;
    /*tex the formula */
    pointer p;
    /*tex box containing equation number */
    pointer a = null;
    /*tex `\.{\\leqno}' instead of `\.{\\eqno}' */
    boolean l = false;
    m = mode;
    /*tex this pops the nest */
    p = fin_mlist(null);
    if (cur_cmd == math_shift_cs_cmd &&
        (cur_chr == text_style || cur_chr == display_style)) {
        you_cant();
    }
    if (mode == -m) {
        /*tex end of equation number */
        if (cur_cmd == math_shift_cmd) {
            check_second_math_shift();
        } else {
            check_display_math_end();
        }
        run_mlist_to_hlist(p, false, text_style);
        a = hpack(vlink(temp_head), 0, additional, -1);
        build_attribute_list(a);
        unsave_math();
        /*tex now |cur_group=math_shift_group| */
        decr(save_ptr);
        assert(saved_type(0) == saved_eqno);
        if (saved_value(0) == 1)
            l = true;
        m = mode;
        p = fin_mlist(null);

    }
    if (m < 0) {
        /*tex

            The |unsave| is done after everything else here; hence an appearance
            of `\.{\\mathsurround}' inside of `\.{\$...\$}' affects the spacing
            at these particular \.\$'s. This is consistent with the conventions
            of `\.{\$\$...\$\$}', since `\.{\\abovedisplayskip}' inside a display
            affects the space above that display.

        */
        if (cur_cmd == math_shift_cs_cmd) {
            check_inline_math_end();
        }
        tail_append(new_math(math_surround_par, before));
        /*tex begin mathskip code */
        switch (math_skip_mode) {
            case 0 :
                /*tex obey mathsurround when zero glue */
                if (! glue_is_zero(math_skip_par)) {
                    copy_glue_values(tail,math_skip_par);
                    surround(tail) = 0;
                }
                break ;
            case 1 :
                /*tex always left */
            case 3 :
                /*tex always both */
            case 6 :
                /*tex only when skip */
                copy_glue_values(tail,math_skip_par);
                surround(tail) = 0;
                break ;
            case 2 :
                /*tex only right */
                surround(tail) = 0;
                break ;
            case 4 :
                /*tex ignore, obey marthsurround */
                break ;
            case 5:
                /*tex all spacing disabled */
                surround(tail) = 0;
                break ;
        }
        /*tex end mathskip code */
        if (dir_math_save) {
            tail_append(new_dir(math_direction_par));
        }
        run_mlist_to_hlist(p, (mode > 0), text_style);
	try_couple_nodes(tail,vlink(temp_head));

        while (vlink(tail) != null) {
            tail = vlink(tail);
        }
        if (dir_math_save) {
            tail_append(new_dir(math_direction_par));
            subtype(tail) = cancel_dir;
        }
        dir_math_save = false;
        tail_append(new_math(math_surround_par, after));
        /*tex begin mathskip code */
        switch (math_skip_mode) {
            case 0 :
                /*tex obey mathsurround when zero glue */
                if (! glue_is_zero(math_skip_par)) {
                    copy_glue_values(tail,math_skip_par);
                    surround(tail) = 0;
                }
                break ;
            case 2 :
                /*tex always right */
            case 3 :
                /*tex always both */
            case 6 :
                /*tex only when skip */
                copy_glue_values(tail,math_skip_par);
                surround(tail) = 0;
                break ;
            case 1 :
                /*tex only left */
                surround(tail) = 0;
                break ;
            case 4 :
                /*tex ignore, obey marthsurround */
                break ;
            case 5:
                /*tex all spacing disabled */
                surround(tail) = 0;
                break ;
        }
        /*tex end mathskip code */
        space_factor_par = 1000;
        unsave_math();
    } else {
        if (a == null) {
            if (cur_cmd == math_shift_cmd) {
                check_second_math_shift();
            } else {
                check_display_math_end();
            }
        }
        run_mlist_to_hlist(p, false, display_style);
        finish_displayed_math(l, a, vlink(temp_head));
    }
}

/*tex

    When \.{\\halign} appears in a display, the alignment routines operate
    essentially as they do in vertical mode. Then the following program is
    activated, with |p| and |q| pointing to the beginning and end of the
    resulting list, and with |aux_save| holding the |prev_depth| value.

*/

void finish_display_alignment(pointer p, pointer q, halfword saved_prevdepth)
{
    do_assignments();
    if (cur_cmd == math_shift_cmd) {
        check_second_math_shift();
    } else {
        check_display_math_end();
    }
    pop_nest();
    tail_append(new_penalty(pre_display_penalty_par,before_display_penalty));
    inject_display_skip_before(above_display_skip_code);
    vlink(tail) = p;
    if (p != null)
        tail = q;
    tail_append(new_penalty(post_display_penalty_par,after_display_penalty));
    inject_display_skip_after(below_display_skip_code);
    cur_list.prev_depth_field = saved_prevdepth;
    resume_after_display();
}

/*tex Interface to \.{\\Umath} and \.{\\mathstyle}: */

void setup_math_style(void)
{
    pointer q;
    tail_append(new_noad());
    q = new_node(math_char_node, 0);
    nucleus(tail) = q;
    (void) scan_math_style(nucleus(tail), num_style(m_style));
}

void print_math_style(void)
{
    if (abs(mode) == mmode)
        print_int(m_style);
    else
        print_int(-1);
}