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+%% @texfile{
+%% author = "Karl Berry and Oren Patashnik",
+%% version = "0.99p",
+%% date = "30 May 2019",
+%% filename = "btxmac.tex",
+%% address = "tex-eplain@tug.org",
+%% supported = "yes",
+%% docstring = "Defines macros that make BibTeX work with plain TeX",
+%% }
+% BibTeX-for-TeX macros for BibTeX 0.99c, TeX 3.0 or later.
+% Copyright 1990, 1991, 1992, 1995, 2005, 2007, 2013, 2016, 2019 Karl Berry &
+% Oren Patashnik.
+%
+% Unlimited copying and redistribution of this file are permitted as
+% long as this file is not modified. Modifications (and redistribution
+% thereof) are permitted, but only if the resulting file is not named
+% btxmac.tex.
+%
+% This file contains TeX macros that allow BibTeX, a bibliography
+% program that was originally designed for use with LaTeX, to work with
+% plain TeX. Please report any bugs (outright goofs, improvable macros,
+% misfeatures, or unclear documentation) to Oren Patashnik
+% (opbibtex@cs.stanford.edu). These macros will become frozen shortly
+% after BibTeX version 1.00 is released.
+%
+% AMS-TEX WARNING: We tried very hard, as of version .99i of these macros,
+% to make them compatible with AmS-TeX. We succeeded to the extent
+% that, if you use one of the standard bibliography styles, you probably
+% won't notice any problems with version 0.99i of btxmac.tex. But
+% ultimately we failed, in that the inherent incompatibilities between
+% plain TeX and AmS-TeX kept making these macros break, for certain
+% inputs or certain styles. Examples: (1) AmS-TeX treats at-signs as
+% special, in ways that plain TeX and LaTeX don't, so that, for example,
+% you can't have any `@' characters in an argument to the \cite command,
+% the way you can in TeX or LaTeX; (2) AmS-TeX decided that plain TeX's
+% and LaTeX's macron-accent control sequence `\=' should be undefined;
+% so you'll need to define `\=' to be `\B' to get the xampl.bib example
+% suggested below to work with AmS-TeX; (3) AmS-TeX redefines the tie
+% character `~' of plain TeX, and AmS-TeX's `amsppt' style redefines
+% plain TeX's `\nobreak' macro, so that if you use an author-date style
+% like `apalike' and you have a multiple-author reference for which the
+% author-date style automatically produces a citation in the text like
+% `(Jones et~al., 1992)' you will throw AmS-TeX's `amsppt' style into
+% an infinite loop, exceeding its input stack size.
+%
+% In practice, such incompatibilities surface infrequently; but it is
+% now clear to us that it's not worth the effort (perhaps it's not even
+% possible) to make the btxmac.tex macros robust when used both with
+% plain TeX and Ams-TeX. If the BibTeX/AmS-TeX results attainable with
+% the current btxmac.tex macros are sufficient, fine. But if there's a
+% demand for more robust BibTeX/AmS-TeX behavior, then someone who's
+% very familiar with the AmS-TeX package should probably make an
+% amsbtxmc.tex version of the macros. Until then, if you're an AmS-TeX
+% user, or a LaTeX or plain TeX user sharing files with an AmS-TeX user,
+% beware.
+% END OF AMS-TEX WARNING.
+%
+% To use these macros you should be familiar with how BibTeX interacts
+% with LaTeX, since BibTeX's interaction with TeX is very similar; that
+% interaction is explained in the LaTeX manual. It also helps to
+% have read "BibTeXing", the documentation that accompanies BibTeX.
+%
+% Then, if you want, you should redefine any of the macros that begin
+% with `\bbl' or `\biblabel' or `\print' that you need to get formatting
+% different from the default (the default settings are designed to
+% accompany a bibliography style like BibTeX's standard style `plain').
+% The macros you might want to change are described briefly a few
+% paragraphs hence.
+%
+% To get started without reading any documentation, try running the
+% short .tex file below through TeX and BibTeX.
+%
+% Remember the general scheme: Running (La)TeX writes information on the
+% .aux (auxiliary) file; then running BibTeX reads information from the
+% .aux, .bst (style), and .bib (database) files, and writes information
+% (the bibliography) on a .bbl file; then running (La)TeX incorporates
+% the bibliography; then running (La)TeX once more fixes the remaining
+% forward references into the bibliography. Thus, to get everything
+% incorporated into your output, you'll have to run (La)TeX, BibTeX,
+% (La)TeX, (La)TeX. (Standup, sitdown, fight, fight, fight.)
+%
+% These macros can stand alone or they can be \input into a macro
+% package, like Eplain, that is sufficiently compatible with plain TeX.
+% To use these macros to format the 0.99 version of the xampl.bib file
+% that's distributed with BibTeX (that version of the file has no
+% self-identification), you'll need to define \mbox, which is a LaTeX
+% command, to be \hbox, as in the example below.
+%
+% Here's an eight-line plain TeX file for trying out btxmac.tex; of course
+% you'll have to remove the comment characters at the beginning of each
+% line, and, depending on your system, you might have to take steps so
+% that BibTeX can "see" the files xampl.bib and plain.bst (BibTeX will
+% give you two empty-field warning messages that you should ignore).
+%
+% \input btxmac
+% \noindent This cites Aamport's gnominious article~\cite{article-full}.
+% \medskip
+% \leftline{\bf References}
+% \nocite{*} % put all database entries into the reference list
+% \bibliographystyle{plain} % specify plain.bst as the style file
+% \bibliography{xampl} % specify the database files; here, just xampl.bib
+% \bye
+%
+%
+% HISTORY
+%
+% Karl Berry wrote the original version of these macros in 1989 and
+% 1990, for use in his `Eplain' package. Oren Patashnik modified them
+% slightly in July 1990, as part of the official BibTeX distribution.
+%
+% 1-Aug-90 Version 0.99a, not released to the general public.
+% 14-Aug-90 0.99b, first general release.
+% 26-Aug-90 0.99c, made \@undefinedmessage work with other macro packages.
+% 6-Sep-90 0.99d, allowed for general formatting of bibliography labels,
+% for general formatting of (in-text) citations, and for
+% changing certain catcodes while reading the .aux file.
+% 14-Nov-90 0.99e, changed the way \@setletters works, made some \new...'s
+% non-outer, and changed the way Eplain reads this file.
+% 12-Dec-90 0.99f, made \@resetnumerals change the `,' and `.' catcodes; and
+% added \biblabelextrahang, \@getoptionalarg, and \bblsc.
+% 11-Mar-91 0.99g, made a few minor changes required by the way Eplain reads
+% this file, but no functional changes.
+% 24-Apr-91 0.99h, inhibited the reading and writing of the .aux file if it
+% isn't used or if the \noauxfile macro is defined, and
+% removed some .aux-file-opening detritus; printed the
+% cite-key of undefined citations in \tt font; changed the
+% catcode of `_' inside \cite; and called \@resetnumerals
+% from inside a group.
+% 29-Feb-92 0.99i, made these macros semi-compatible with AmS-TeX; removed
+% \@resetnumerals, \@setletters, \@tokstostring, and
+% friends; changed the way \cite handles catcodes; changed
+% \@getoptionalarg, and had \bibitem and \newcommand use
+% it; added \@futurenonspacelet and (to facilitate the use
+% of multiple reference lists) \bblfilebasename; changed
+% \biblabelprint to use the new macros \biblabelprecontents
+% and \biblabelpostcontents, and to, by default, right-
+% justify numeric labels; and renamed \biblabelextrahang to
+% the more descriptive \biblabelextraspace.
+% 14-Mar-92 0.99j, made 0.99i's use of `\\' local to btxmac.tex.
+% 13-Nov-95 0.99k, defined \begin and \end (while reading bbl file) only if
+% it wasn't already defined.
+% 11-Aug-03 0.99l, defined \renewcommand and \providecommand, since some AMS
+% style files use them. Also defined \emph, \textbf, and
+% \mbox, since many .bib files use them. This version was
+% never actually released, but these changes appear
+% starting with 0.99k-18aug05.
+% 18-Aug-05 0.99k-18aug05, made the \em, \emph, etc., definitions effective
+% only if not already defined. Provided
+% \printcite{pre,post}item, \bblitemhook.
+% 09-Sep-07 0.99k-09sep07, executed \@citedef in a group to avoid potential
+% save-stack overflow.
+% 07-Feb-13 0.99m, made \newcommand and \providecommand be \long, and not
+% use \edef. Defined \bbltextbf.
+% 30-Sep-13 0.99n, made \@futurenonspacelet be \long,
+% renamed \@optionaltemp to \@optionalusercs,
+% ignored spaces after the optional argument.
+% 12-May-16 0.99o, renamed \@newcommand and others to \@btx..., to avoid
+% conflict with Babel's file plain.def.
+% 30-May-19 0.99p, one missed rename of \@continuenewcommand to \@btx...,
+% that made \providecommand fail.
+%
+% The LaTeX-related commands defined in this file include
+% (a) the four commands that a user types (\bibliography,
+% \bibliographystyle, \cite, and \nocite);
+% (b) three commands that BibTeX looks for in the .aux
+% file (\bibdata, \bibstyle, and \citation---there is a fourth command
+% that BibTeX looks for, but that command is related to LaTeX's \include
+% facility, so these macros ignore that command); and
+% (c) the LaTeX commands (\newcommand, \renewcommand, \providecommand)
+% that are written by a standard (alpha) or AMS bibliography style.
+% (d) a few more LaTeX commands (\emph, \mbox, \textbf) which many .bib
+% files use.
+%
+% The definitions here are not the same as the corresponding LaTeX
+% definitions (those LaTeX definitions depend on a significant fraction
+% of LaTeX itself). But the only significant differences are with the
+% \*command macros, which in LaTeX (a) give warnings in various
+% circumstances; (b) allow a second optional argument; and (c) make the
+% defined control sequences \long. The versions here don't do any of
+% those things.
+%
+% To summarize: Unless you know what you're doing, you shouldn't define
+% any control sequences with these ten names:
+%
+% \bibdata
+% \bibliography
+% \bibliographystyle
+% \bibstyle
+% \citation
+% \cite
+% \newcommand
+% \nocite
+% \providecommand
+% \renewcommand
+%
+% There are other commands written by one or more of the four standard
+% (plain, abbrv, alpha, unsrt) or four semistandard (acm, apalike,
+% ieeetr, siam) bibliography styles, or commonly used in .bib files.
+% These take effect only within the bibliography, and are redefinable,
+% as explained later:
+%
+% \em
+% \emph
+% \mbox
+% \newblock
+% \sc
+% \textbf
+%
+% There's one control sequence you might want to use (but not redefine)
+% in redefining \biblabelprint:
+%
+% \biblabelwidth
+%
+% There are fifteen other control sequences (explained later in more detail)
+% that the macros of this file will use if you define them---you should
+% define them after the \input btxmac command but before the \bibliography
+% command. The first six begin with `\bbl' and affect fonts, spacing,
+% perhaps other characteristics of the bibliography, and which .bbl files
+% get read; the next five begin with `\biblabel' and determine how labels
+% are formatted in the bibliography; and the last four begin with `\print'
+% and determine how the in-text citations are formatted:
+%
+% \bblem
+% \bblfilebasename
+% \bblhook
+% \bblnewblock
+% \bblrm
+% \bblsc
+% \biblabelcontents
+% \biblabelprecontents
+% \biblabelprint
+% \biblabelpostcontents
+% \biblabelextraspace
+% \printbetweencitations
+% \printcitefinish
+% \printcitenote
+% \printcitestart
+%
+% If it's defined before the \input btxmac command, the control sequence
+% below inhibits the reading and writing of the .aux file(s), and the
+% issuing of related warning messages. Any definition will do. This
+% feature might help when you're working on draft stages of a document:
+%
+% \noauxfile
+%
+%
+% Here's another control sequence (it's described later) that you
+% probably won't want to redefine unless you are writing another macro
+% package; if you do redefine it, however, do it before the \input btxmac
+% command (and notice that it has an `@' in its name):
+%
+% \@undefinedmessage
+%
+% Any other control sequence in this file that might conflict with
+% something you've defined will have an `@' in its name, so such conflicts
+% are unlikely; but if you're worried about a specific control sequence
+% name, do a text search of this file to look for it.
+%
+%
+% So to start things off we turn `@' into a letter (category code 11),
+% keeping track of the old category code for future restoration.
+% (Simply resetting it to 12 when we leave these macros is
+% insufficient.) We use `\cite' as a temporary control sequence to
+% save the current catcode of @ to avoid possibly overwriting something
+% (without an `@' in its name) that might already be defined.
+%
+\edef\cite{\the\catcode`@}%
+\catcode`@ = 11
+\let\@oldatcatcode = \cite
+\chardef\@letter = 11
+\chardef\@other = 12
+%
+%
+% Next come some things that will be useful later.
+%
+% Make an outer definition into an inner one (due to Chris Thompson).
+% The arguments should be the control sequence to be defined, and the
+% new of the \outer control sequence, as characters; the control
+% sequence #1 is defined to be just the same as \csname#2\endcsname, but
+% not \outer. For example, \@innerdef\innernewcount{newcount} would
+% define \innernewcount to be a non-outer version of \newcount.
+%
+\def\@innerdef#1#2{\edef#1{\expandafter\noexpand\csname #2\endcsname}}%
+%
+% We use \@innerdef to make some of our allocations local, because
+% Eplain includes our code inside a conditional. We put @'s in the
+% names to minimize the (already small) chance of conflicts.
+%
+\@innerdef\@innernewcount{newcount}%
+\@innerdef\@innernewdimen{newdimen}%
+\@innerdef\@innernewif{newif}%
+\@innerdef\@innernewwrite{newwrite}%
+%
+%
+% Swallow one parameter.
+%
+\def\@gobble#1{}%
+%
+%
+% Use TeX 3.0's \inputlineno to get the line number, for better error
+% messages, but if we're using an old version of TeX, don't do anything.
+%
+\ifx\inputlineno\@undefined
+ \let\@linenumber = \empty % Pre-3.0.
+\else
+ \def\@linenumber{\the\inputlineno:\space}%
+\fi
+%
+%
+% The following macro \@futurenonspacelet (from the TeXbook) behaves
+% essentially like \futurelet except that it discards any implicit or
+% explicit space tokens that intervene before a nonspace is scanned:
+%
+\long\def\@futurenonspacelet#1{\def\cs{#1}%
+ \afterassignment\@stepone\let\@nexttoken=
+}%
+\begingroup % The grouping here avoids stepping on an outside use of `\\'.
+\def\\{\global\let\@stoken= }%
+\\ % now \@stoken is a space token (\\ is a control symbol, so that
+ % space after it is seen).
+\endgroup
+\def\@stepone{\expandafter\futurelet\cs\@steptwo}%
+\def\@steptwo{\expandafter\ifx\cs\@stoken\let\@@next=\@stepthree
+ \else\let\@@next=\@nexttoken\fi \@@next}%
+\def\@stepthree{\afterassignment\@stepone\let\@@next= }%
+%
+%
+% \@getoptionalarg\CS gets an optional argument from the input, enclosed
+% in brackets, then expands \CS. We set \@optionalarg to \empty if we
+% don't find one, otherwise to the text of the argument. This assumes
+% the brackets don't have a funny category code.
+%
+\def\@getoptionalarg#1{%
+ \let\@optionalusercs = #1%
+ \let\@optionalnext = \relax
+ \@futurenonspacelet\@optionalnext\@bracketcheck
+}%
+%
+% The \expandafter's in this macro let us avoid the use of \aftergroup,
+% which is somewhat more expensive.
+%
+\def\@bracketcheck{%
+ \ifx [\@optionalnext
+ \expandafter\@@getoptionalarg % we have an optional arg
+ \else
+ \let\@optionalarg = \empty % no optional arg
+ \expandafter\@optionalusercs
+ \fi
+}%
+%
+% Get the next bracketed text.
+\def\@@getoptionalarg[#1]{%
+ \def\@optionalarg{#1}%
+ % Ignore spaces after the optional arg, too.
+ % (We don't actually need to peek ahead, but this is the easiest way
+ % to ignore the spaces.)
+ \let\@optdummy=\relax % just in case it has become \outer somehow
+ \@futurenonspacelet\@optdummy\@optionalusercs
+}%
+%
+%
+% From LaTeX.
+%
+\def\@nnil{\@nil}%
+\def\@fornoop#1\@@#2#3{}%
+%
+\def\@for#1:=#2\do#3{%
+ \edef\@fortmp{#2}%
+ \ifx\@fortmp\empty \else
+ \expandafter\@forloop#2,\@nil,\@nil\@@#1{#3}%
+ \fi
+}%
+%
+\def\@forloop#1,#2,#3\@@#4#5{\def#4{#1}\ifx #4\@nnil \else
+ #5\def#4{#2}\ifx #4\@nnil \else#5\@iforloop #3\@@#4{#5}\fi\fi
+}%
+%
+\def\@iforloop#1,#2\@@#3#4{\def#3{#1}\ifx #3\@nnil
+ \let\@nextwhile=\@fornoop \else
+ #4\relax\let\@nextwhile=\@iforloop\fi\@nextwhile#2\@@#3{#4}%
+}%
+%
+%
+% This macro tests if a file \jobname.#1 exists, and sets \if@fileexists
+% appropriately. If an optional argument is given, it is used as the
+% root part of the filename instead of \jobname.
+%
+\@innernewif\if@fileexists
+%
+\def\@testfileexistence{\@getoptionalarg\@finishtestfileexistence}%
+\def\@finishtestfileexistence#1{%
+ \begingroup
+ \def\extension{#1}%
+ \immediate\openin0 =
+ \ifx\@optionalarg\empty\jobname\else\@optionalarg\fi
+ \ifx\extension\empty \else .#1\fi
+ \space
+ \ifeof 0
+ \global\@fileexistsfalse
+ \else
+ \global\@fileexiststrue
+ \fi
+ \immediate\closein0
+ \endgroup
+}%
+%
+%
+%% [[[start of BibTeX-specific stuff]]]
+%
+% Now come the four main LaTeX commands and their associated .aux
+% commands. Just as in LaTeX, \bibliographystyle defines the BibTeX
+% style name (.bst file, that is), and \bibliography defines the
+% database (.bib) file(s). The corresponding .aux-file commands are
+% \bibstyle and \bibdata, which are there only for BibTeX's (but not
+% LaTeX's) use.
+%
+\def\bibliographystyle#1{%
+ \@readauxfile
+ \@writeaux{\string\bibstyle{#1}}%
+}%
+\let\bibstyle = \@gobble
+%
+% As well as writing the \bibdata command to tell BibTeX which .bib
+% files to read, we read the .bbl file that BibTeX (or a person,
+% conceivably) has produced. We use \bblfilebasename as the root of the
+% filename to read; this defaults to \jobname.
+%
+\let\bblfilebasename = \jobname
+\def\bibliography#1{%
+ \@readauxfile
+ \@writeaux{\string\bibdata{#1}}%
+ \@testfileexistence[\bblfilebasename]{bbl}%
+ \if@fileexists
+ % We just output a non-discardable item (the `whatsit' with the
+ % \bibdata command). This means that the glue that will be
+ % inserted next (\parskip or \baselineskip, most likely) will be a
+ % legal breakpoint. Most likely, this is after some kind of
+ % heading, where we don't want to allow a page break. So:
+ \nobreak
+ \@readbblfile
+ \fi
+}%
+\let\bibdata = \@gobble
+%
+% The \nocite{label,label,...} command writes its argument to \@auxfile,
+% unless instructed not to, but produces no text in the document. Both
+% the \nocite and \cite commands produce \citation commands in the .aux file.
+%
+\def\nocite#1{%
+ \@readauxfile
+ \@writeaux{\string\citation{#1}}%
+}%
+%
+\@innernewif\if@notfirstcitation
+%
+% \cite[note]{label,label,...} produces the citations for the labels as
+% well. If the optional argument `note' is present, it's added after
+% the labels. Since \cite calls \nocite to do its .aux-file writing,
+% \cite doesn't need to call \@readauxfile (\nocite does).
+%
+\def\cite{\@getoptionalarg\@cite}%
+%
+% Typeset the citations for the labels in #1, followed by the note, if
+% it exists. To change the citation's format in the text, redefine one
+% or more `\print...' macros, whose defaults appear later in this file.
+%
+\def\@cite#1{%
+ % Remember the optional argument, in case one of the macros we call
+ % below ends up looking for an optional argument itself. For
+ % example, if a \cite[note] triggers reading the .aux file, then the
+ % [note] would be clobbered, since \@testfileexistence looks for an
+ % optional arg.
+ \let\@citenotetext = \@optionalarg
+ % Start printing the text, beginning with a left bracket by default.
+ \printcitestart
+ % It's complicated, but because \nocite puts a `whatsit' onto the list,
+ % \nocite should follow \printcitestart. It's conceivable, but very
+ % unlikely, that this `whatsit' will cause a problem (glue that doesn't
+ % disappear when you want it to is the most likely symptom), requiring
+ % a change either to \printcitestart or to the label that the .bst file
+ % produces.
+ \nocite{#1}%
+ \@notfirstcitationfalse
+ \@for \@citation :=#1\do
+ {%
+ \expandafter\@onecitation\@citation\@@
+ }%
+ \ifx\empty\@citenotetext\else
+ \printcitenote{\@citenotetext}%
+ \fi
+ \printcitefinish
+}%
+%
+\def\@onecitation#1\@@{%
+ \if@notfirstcitation
+ \printbetweencitations
+ \fi
+ %
+ \expandafter \ifx \csname\@citelabel{#1}\endcsname \relax
+ \if@citewarning
+ \message{\@linenumber Undefined citation `#1'.}%
+ \fi
+ % Give it a dummy definition:
+ \expandafter\gdef\csname\@citelabel{#1}\endcsname{%
+ {\tt
+ \escapechar = -1
+ \nobreak\hskip0pt
+ \expandafter\string\csname#1\endcsname
+ \nobreak\hskip0pt
+ }%
+ }%
+ \fi
+ % Now produce the text, whether it was undefined or not.
+ \printcitepreitem{#1}%
+ \csname\@citelabel{#1}\endcsname
+ \printcitepostitem
+ \@notfirstcitationtrue
+}%
+%
+% Given a label `foo', the macro `\b@foo' is supposed to
+% hold the text that should be produced.
+%
+\def\@citelabel#1{b@#1}%
+%
+% So, how does a citation label get defined? When we read the .bbl file
+% (below), a \bibitem writes out a \@citedef command. And when we read
+% the \@citedef, we define \@citelabel{#1}, where #1 is the user's
+% label.
+%
+% The group around the def will keep the save stack from overflowing:
+% We are reading the .aux file inside a group. For undefined
+% commands, \csname...\endcsname makes them equivalent to \relax
+% locally in that group; when we globally redefine them, TeX enters
+% the definitions on the save stack, once for each label. When done
+% in the topmost group, this can overflow a stack of any size, given
+% sufficient number of label definitions. So, we put these
+% \csname...\endcsname's inside another group, to pop the stack for
+% every label.
+\def\@citedef#1#2{{\expandafter\gdef\csname\@citelabel{#1}\endcsname{#2}}}%
+%
+%
+% Reading the .bbl file also produces the typeset bibliography. Please
+% notice, however, that we do not produce the title for the references
+% (e.g., `References'), as LaTeX does. The formatting and spacing of
+% that title, whether it should go into the headline, and so on, are all
+% things determined by your format. We cannot know those things in
+% advance. If you wish, you can define \bblhook to produce the title.
+% Or just do it before the \bibliography command.
+%
+\def\@readbblfile{%
+ % Define a counter to tell us which item number we are on, unless
+ % we've already defined it (because the document has more than one
+ % bibliography).
+ \ifx\@itemnum\@undefined
+ \@innernewcount\@itemnum
+ \fi
+ %
+ \begingroup
+ % If another package has already defined \begin, don't define our
+ % own simplistic \begin and \end; assume they want to take care of
+ % it themselves. (That way, their \begin's and \end's for other
+ % things can be used in the bib files.)
+ \ifx\begin\@undefined
+ \def\begin##1##2{%
+ % ##1 is just `thebibliography'.
+ % ##2 is the widest label.
+ % We set (new dimen) \biblabelwidth based on the widest label
+ \setbox0 = \hbox{\biblabelcontents{##2}}%
+ \biblabelwidth = \wd0
+ }%
+ \let\end = \@gobble % The arg is `thebibliography' again.
+ \fi
+ %
+ % Here we have two possibilities:
+ % \bibitem[typesetlabel]{citationlabel}
+ % \bibitem{citationlabel}
+ % If we have the second of these, the citations are numbered, starting
+ % from one; we use our own count register \@itemnum for this.
+ %
+ \@itemnum = 0
+ \def\bibitem{\@getoptionalarg\@bibitem}%
+ \def\@bibitem{%
+ \ifx\@optionalarg\empty
+ \expandafter\@numberedbibitem
+ \else
+ \expandafter\@alphabibitem
+ \fi
+ }%
+ \def\@alphabibitem##1{%
+ % Need \xdef here for various reasons.
+ \expandafter \xdef\csname\@citelabel{##1}\endcsname {\@optionalarg}%
+ % Left-justify alpha labels, unless \biblabel{pre,post}contents
+ % are already defined.
+ \ifx\biblabelprecontents\@undefined
+ \let\biblabelprecontents = \relax
+ \fi
+ \ifx\biblabelpostcontents\@undefined
+ \let\biblabelpostcontents = \hss
+ \fi
+ \@finishbibitem{##1}%
+ }%
+ %
+ \def\@numberedbibitem##1{%
+ \advance\@itemnum by 1
+ \expandafter \xdef\csname\@citelabel{##1}\endcsname{\number\@itemnum}%
+ % Right-justify numeric labels, unless \biblabel{pre,post}contents
+ % are already defined.
+ \ifx\biblabelprecontents\@undefined
+ \let\biblabelprecontents = \hss
+ \fi
+ \ifx\biblabelpostcontents\@undefined
+ \let\biblabelpostcontents = \relax
+ \fi
+ \@finishbibitem{##1}%
+ }%
+ %
+ \def\@finishbibitem##1{%
+ \bblitemhook{##1}%
+ \biblabelprint{\csname\@citelabel{##1}\endcsname}%
+ \@writeaux{\string\@citedef{##1}{\csname\@citelabel{##1}\endcsname}}%
+ \ignorespaces
+ }%
+ %
+ % Do the printing (we're producing the bibliography, remember).
+ %
+ \ifx\undefined\em \let\em=\bblem \fi
+ \ifx\undefined\emph \let\emph=\bblemph \fi
+ \ifx\undefined\mbox \let\mbox=\bblmbox \fi
+ \ifx\undefined\newblock \let\newblock=\bblnewblock \fi
+ \ifx\undefined\sc \let\sc=\bblsc \fi
+ \ifx\undefined\textbf \let\textbf=\bbltextbf \fi
+ %
+ % Punctuation won't affect spacing;
+ \frenchspacing
+ % the penalties below are from LaTeX's [article,book,report].sty;
+ \clubpenalty = 4000 \widowpenalty = 4000
+ % the next two values come from LaTeX's \sloppy command;
+ \tolerance = 10000 \hfuzz = .5pt
+ \everypar = {\hangindent = \biblabelwidth
+ \advance\hangindent by \biblabelextraspace}%
+ \bblrm
+ % the \parskip is a guess at what looks good;
+ \parskip = 1.5ex plus .5ex minus .5ex
+ % and the space between label and text comes from LaTeX's \labelsep.
+ \biblabelextraspace = .5em
+ \bblhook
+ %
+ \input \bblfilebasename.bbl
+ \endgroup
+}%
+%
+% The widest label's width is useful for redefining \biblabelprint;
+% you redefine \biblabelwidth, in effect, by redefining the
+% \biblabelcontents macro that appears below. And \biblabelextraspace,
+% which is redefinable inside \bblhook, is added to \biblabelwidth to
+% determine the amount of hanging indentation.
+%
+\@innernewdimen\biblabelwidth
+\@innernewdimen\biblabelextraspace
+%
+% Now come the main macros that are related to the printing of the
+% bibliography. Since you might want to redefine them, they are given
+% default definitions outside of \@readbblfile.
+%
+% The first one controls the printing of a bibliography entry's label.
+% If you change it, make sure that it starts with something like
+% \noindent or \indent or \leavevmode that puts TeX into horizontal mode
+% (even if the label itself is empty); otherwise, the hanging
+% indentation will get messed up in certain circumstances.
+%
+\def\biblabelprint#1{%
+ \noindent
+ \hbox to \biblabelwidth{%
+ \biblabelprecontents
+ \biblabelcontents{#1}%
+ \biblabelpostcontents
+ }%
+ \kern\biblabelextraspace
+}%
+%
+% If you are using numeric labels, and you want them left-justified
+% (numeric labels by default are right-justified), do something like:
+% \def\biblabelprecontents{\relax}
+% \def\biblabelpostcontents{\hss}
+%
+% By default the labels are typeset in \bblrm, and enclosed in brackets.
+\def\biblabelcontents#1{{\bblrm [#1]}}%
+%
+% The main text, too, is typeset using \bblrm, which is \rm by default.
+\def\bblrm{\rm}%
+%
+% Emphasis for producing, e.g., titles, is done with \it by default.
+\def\bblem{\it}%
+%
+% Another way to emphasize, with built-in italic correction. (Doesn't
+% look for a following comma or period, though.)
+\def\bblemph#1{{\bblem #1\/}}
+%
+% And bold.
+\def\bbltextbf#1{{\bf #1}}
+%
+% \mbox is \hbox forcing horizontal mode.
+\def\bblmbox{\leavevmode\hbox}
+%
+% Some styles use a caps-and-small-caps font for author names. LaTeX
+% defines an \sc command but plain TeX doesn't, so we need one here.
+% The definition below doesn't load the font unless it's needed, but it
+% tries to load only the 10pt version, because it might not exist at
+% other point sizes.
+%
+\def\bblsc{\ifx\@scfont\@undefined
+ \font\@scfont = cmcsc10
+ \fi
+ \@scfont
+}%
+%
+% The major parts of an entry are separated with \bblnewblock. The
+% numbers below are taken from LaTeX's `article' style.
+%
+\def\bblnewblock{\hskip .11em plus .33em minus .07em }%
+%
+% Here's where you stick any other bibliography-formatting goodies, or
+% redefine the values above.
+%
+\let\bblhook = \empty
+%
+% And here you can add code to be executed before each item (before
+% \biblabelprint is called). The parameter is citation label for this
+% bibliography entry.
+%
+\let\bblitemhook = \@gobble
+%
+%
+% Here are the four default definitions for formatting the in-text
+% citations. These are what you redefine (after your \input btxmac but
+% before your \bibliography) to get parens instead of brackets, or
+% superscripts, or footnotes, or whatever.
+%
+\def\printcitestart{[}% left bracket
+\def\printcitefinish{]}% right bracket
+\def\printbetweencitations{, }% comma, space
+\let\printcitepreitem\@gobble % takes label
+\let\printcitepostitem\empty
+\def\printcitenote#1{, #1}% comma, space, note (if it exists)
+%
+% That scheme is pretty flexible. For example you could use
+% \def\printcitestart{\unskip $^\bgroup}
+% \def\printcitefinish{\egroup$}
+% \def\printbetweencitations{,}
+% \def\printcitenote#1{\hbox{\sevenrm\space (#1)}}
+% \font\eighttt = cmtt8
+% \scriptfont\ttfam = \eighttt
+% to get superscripted in-text citations. (The scriptfont stuff
+% exists only to print an undefined citation; it's in cmtt8 because
+% there is no cmtt7.) To get something radically different, however,
+% you'll have to define your own \cite command.
+%
+% When we read `\citation' from the .aux file, it means nothing.
+%
+\let\citation = \@gobble
+%
+%
+% Now comes the stuff for dealing with LaTeX's \newcommand. As
+% mentioned earlier, this \newcommand will redefine a preexisting
+% command; that's different from how LaTeX's \newcommand behaves.
+%
+\@innernewcount\@btxnumparams
+%
+% \newcommand{\foo}[n]{text} defines the control sequence \foo to have n
+% parameters, and replacement text `text'. In LaTeX, this command gives
+% a warning if \foo is already defined, and allows a second
+% optional argument (which is a default value for the first optional
+% arg) but we don't bother with either of these.
+%
+\ifx\newcommand\undefined
+\long\def\newcommand#1{%
+ \def\@btxcommandname{#1}%
+ \@getoptionalarg\@btxcontinuenewcommand
+}%
+\fi
+%
+%
+% \renewcommand{\foo}[n]{text}, for our purposes, is the same as
+% \newcommand. In LaTeX, it gives a warning if \foo is not already defined.
+%
+\ifx\renewcommand\undefined
+ \let\renewcommand = \newcommand
+\fi
+%
+%
+% \providecommand{\foo}[n]{text} defines \foo as in \newcommand only if
+% \foo is not already defined.
+%
+\ifx\providecommand\undefined
+\long\def\providecommand#1{%
+ \def\@btxcommandname{#1}%
+ %
+ \expandafter\ifx\@btxcommandname \@undefined
+ \let\cs=\@btxcontinuenewcommand % undefined, so we'll define it
+ \else
+ \let\cs=\@gobble % already defined, so ignore it
+ \fi
+ \@getoptionalarg\cs
+}%
+\fi
+%
+%
+% Figure out if this definition has parameters.
+%
+\def\@btxcontinuenewcommand{%
+ % If no optional argument, we have zero parameters. Otherwise, we
+ % have that many.
+ \@btxnumparams = \ifx\@optionalarg\empty 0\else\@optionalarg \fi \relax
+ \@btxnewcommand
+}%
+%
+% \@btxnumparams is how many arguments this command has. The name of the
+% command is \@btxcommandname. The replacement text for the new macro is #1.
+%
+\def\@btxnewcommand#1{%
+ \def\@btxstartdef{\expandafter\def\@btxcommandname}%
+ \ifnum\@btxnumparams=0
+ \let\@btxparamdef = \empty
+ \else
+ \ifnum\@btxnumparams>9
+ \errmessage{\the\@btxnumparams\space is too many parameters}%
+ \else
+ \ifnum\@btxnumparams<0
+ \errmessage{\the\@btxnumparams\space is too few parameters}%
+ \else
+ \edef\@btxparamdef{%
+ % This is sad, but \loop doesn't work inside \edef,
+ % because \body isn't defined.
+ \ifcase\@btxnumparams
+ \empty No arguments.
+ \or ####1%
+ \or ####1####2%
+ \or ####1####2####3%
+ \or ####1####2####3####4%
+ \or ####1####2####3####4####5%
+ \or ####1####2####3####4####5####6%
+ \or ####1####2####3####4####5####6####7%
+ \or ####1####2####3####4####5####6####7####8%
+ \or ####1####2####3####4####5####6####7####8####9%
+ \fi
+ }%
+ \fi
+ \fi
+ \fi
+ \expandafter\@btxstartdef\@btxparamdef{#1}%
+}%
+%
+%% [[[end of BibTeX-specific stuff]]]
+%
+%
+% Names of references (arguments given in the \cite and \nocite
+% commands) and file names (arguments given in the \bibliography and
+% \bibliographystyle commands) are recorded in \jobname.aux, called the
+% \@auxfile in these macros. Here's how they get read in.
+%
+\def\@readauxfile{%
+ \if@auxfiledone \else % remember: \@auxfiledonetrue if \noauxfile is defined
+ \global\@auxfiledonetrue
+ \@testfileexistence{aux}%
+ \if@fileexists
+ \begingroup
+ % Because we might be in horizontal mode when \@readauxfile
+ % is called (if it's in response to a \cite or \nocite), we
+ % want to ignore all the would-be spaces at the ends of
+ % lines in the aux file. Fortunately, it's highly unlikely
+ % an end-of-line might actually be desired.
+ % And because we don't change the category code of anything
+ % but @, primitives like \gdef can't be used to define labels
+ % in the aux file. The solution adopted by btxmac.tex is to
+ % write `\@citedef{LABEL}{DEFINITION}' to the aux file, and
+ % use \csname on LABEL.
+ \endlinechar = -1
+ \catcode`@ = 11
+ \input \jobname.aux
+ \endgroup
+ \else
+ \message{\@undefinedmessage}%
+ \global\@citewarningfalse
+ \fi
+ \immediate\openout\@auxfile = \jobname.aux
+ \fi
+}%
+%
+% The \@readauxfile macro does all that work the first time it's called.
+% Since it's called once for every \cite, \nocite, \bibliography, and
+% \bibliographystyle command that the user issues, we need to remember
+% whether the work's been done. It's considered done if we're not to do
+% it---that is, if \noauxfile is defined.
+%
+\newif\if@auxfiledone
+\ifx\noauxfile\@undefined \else \@auxfiledonetrue\fi
+%
+% It's conceivable you'd want to change how other characters are read;
+% to do that, change their category code before doing \input btxmac.
+%
+%
+% After reading the .aux file, \@readauxfile opens it for writing.
+% The \@writeaux macro does the actual writing (as long as
+% \noauxfile is undefined).
+%
+\@innernewwrite\@auxfile
+\def\@writeaux#1{\ifx\noauxfile\@undefined \write\@auxfile{#1}\fi}%
+%
+%
+% A macro package that uses btxmac.tex might define
+% \@undefinedmessage (before doing an \input btxmac).
+%
+\ifx\@undefinedmessage\@undefined
+ \def\@undefinedmessage{No .aux file; I won't give you warnings about
+ undefined citations.}%
+\fi
+%
+% Even if citations are undefined, we want to complain only if
+% \@citewarningtrue. The default is to set \@citewarningtrue unless
+% \noauxfile is defined. Again, a macro package that uses
+% btxmac.tex might want to redefine this.
+%
+\@innernewif\if@citewarning
+\ifx\noauxfile\@undefined \@citewarningtrue\fi
+%
+%
+% Finally, before leaving we restore @'s old category code.
+%
+\catcode`@ = \@oldatcatcode