% \iffalse meta-comment
%
% Copyright (C) 1989-1992 by Frank Mittelbach.  All rights reserved.
% 
% This file is part of the multicol package.
% 
% IMPORTANT NOTICE:
% 
% You are not allowed to change this file.  You may however copy this
% file to a file with a different name and then change the copy if you
% obey the restrictions on file changes described in readme.mz.
% 
% You are NOT ALLOWED to distribute this file alone.  You are NOT
% ALLOWED to take money for the distribution or use of this file (or a
% changed version) except for a nominal charge for copying etc.
% 
% You are allowed to distribute this file under the condition that it is
% distributed together with all files mentioned in readme.mz2.
% 
% If you receive only some of these files from someone, complain!
% 
% However, if these files are distributed by established suppliers as
% part of a complete TeX distribution, and the structure of the
% distribution would make it difficult to distribute the whole set of
% files, *those parties* are allowed to distribute only some of the
% files provided that it is made clear that the user will get a complete
% distribution-set upon request to that supplier (not me).  Notice that
% this permission is not granted to the end user.
% 
% 
% For error reports in case of UNCHANGED versions see readme.mz
% 
% 
% \fi

\def\fileversion{v2.1c}
\def\filedate{92/06/22}
\def\docdate {92/06/22}

%% \CheckSum{528}
%% \CharacterTable
%%  {Upper-case    \A\B\C\D\E\F\G\H\I\J\K\L\M\N\O\P\Q\R\S\T\U\V\W\X\Y\Z
%%   Lower-case    \a\b\c\d\e\f\g\h\i\j\k\l\m\n\o\p\q\r\s\t\u\v\w\x\y\z
%%   Digits        \0\1\2\3\4\5\6\7\8\9
%%   Exclamation   \!     Double quote  \"     Hash (number) \#
%%   Dollar        \$     Percent       \%     Ampersand     \&
%%   Acute accent  \'     Left paren    \(     Right paren   \)
%%   Asterisk      \*     Plus          \+     Comma         \,
%%   Minus         \-     Point         \.     Solidus       \/
%%   Colon         \:     Semicolon     \;     Less than     \<
%%   Equals        \=     Greater than  \>     Question mark \?
%%   Commercial at \@     Left bracket  \[     Backslash     \\
%%   Right bracket \]     Circumflex    \^     Underscore    \_
%%   Grave accent  \`     Left brace    \{     Vertical bar  \|
%%   Right brace   \}     Tilde         \~}
%% 
% \iffalse
%
% Style-option `theorem' to use with LaTeX v2.09
% Copyright (C) 1989-1992 Frank Mittelbach, all rights reserved.
%
% For error reports for UNCHANGED versions see readme.
%
% \fi
%
%
% \changes{v1.0}{87/05/07}{First draft.}
% \changes{v1.0a}{87/05/07}{`thistheoremstyle' added.}
% \changes{v1.1a}{87/07/29}{New concept: redefine the internal
%                          \protect\LaTeX{} commands `@xnthm' etc.}
% \changes{v1.1b}{87/07/31}{`theoremfont' used to specify font.}
% \changes{v1.2a}{88/01/08}{`@endtheorem' now globally defined.}
% \changes{v1.2b}{88/01/11}{`newtheorem' only allowed in the preamble.}
% \changes{v1.3a}{88/02/14}{`theoremfont' now a toks register.}
%
% \changes{v2.0a}{88/11/16}{New implementation and new documentation.}
% \changes{v2.0a}{88/11/16}{No layout changes but internal modifications
%                           old substyles won't work.}
% \changes{v2.0b}{89/01/30}{`global' used for all definitions.}
% \changes{v2.0c}{89/06/15}{Documentation translated to English.
%                            Thanks to LLL and Nina}
% \changes{v2.1a}{90/02/15}{Support for new font selection.}
%
% \DoNotIndex{\@endparenv,\@ifdefinable,\@ifnextchar,\@ifundefined}
% \DoNotIndex{\@namedef,\@nameuse,\@spaces,\@tempa,\@warning}
% \DoNotIndex{\ }
% \DoNotIndex{\begingroup,\bf}
% \DoNotIndex{\csname}
% \DoNotIndex{\def,\do,\docdate}
% \DoNotIndex{\endcsname,\endgroup,\endinput,\endtrivlist,\expandafter}
% \DoNotIndex{\filedate,\fileversion}
% \DoNotIndex{\gdef,\global}
% \DoNotIndex{\hbox,\hskip}
% \DoNotIndex{\ignorespaces,\input,\it,\item}
% \DoNotIndex{\labelsep,\let,\llap}
% \DoNotIndex{\makeatletter}
% \DoNotIndex{\noexpand}
% \DoNotIndex{\refstepcounter,\relax,\rlap}
% \DoNotIndex{\setlength,\sl,\space,\string,\strut}
% \DoNotIndex{\the,\trivlist,\typeout}
% \DoNotIndex{\vbox}
% \DoNotIndex{\xdef}
%
% \def\deflabel#1{\tt #1\hfill}
% \def\deflist#1{\begin{list}{}{\settowidth\labelwidth{\tt #1}%
%                               \setlength\leftmargin\labelwidth
%                               \addtolength\leftmargin\labelsep
%                               \let\makelabel\deflabel}}
% \def\enddeflist{\end{list}}
% \def\envfont{\tt}
%
% \MakeShortVerb{\|}
%
% \newcommand{\TUB}{{\sl TUGboat\/}}
%
% \title{An Extension of the
%        \LaTeX{} theorem environment\thanks{This file
%        has version number \fileversion, last
%        revised \filedate, documentation dated \docdate.}}
% \author{Frank Mittelbach\\
%       Electronic Data Systems\\
%         (Deutschland) GmbH\\
%       Eisenstra\ss e 56\\
%       D-6090 R\"usselsheim\\
%       Federal Republic of Germany}
%
% \maketitle
%
% \begin{abstract}
%    The macros described in this paper yield an extension of the
%    \LaTeX{} theorem mechanism. It is designed is to satisfy the
%    different requirements of various journals. Thus, the
%    layout of the ``theorems'' can be manipulated by determining a
%    ``style''. This article describes not only the use, but
%    also the definition, of the necessary macros.
% \end{abstract}
%
% \section*{Preface to version 2.1}
%
% This version is identical to 2.0g described in \TUB\ 10\#3 except
% for some internal defaults which are now set depending on the used
% font selection scheme.
%
% This was done to avoid unpleasant surprises if the new font selection
% scheme is in force. For further details see
% section~\ref{sec:newfonts} and \cite{fs-basics,fs-latex}.
%
% \section{Introduction}
%
% For our purposes here, ``theorems'' are labelled enunciations,
% often set off from the main text by extra space and a font change.
% Theorems, corollaries, conjectures, definitions, and remarks
% are all instances of ``theorems''.  The ``header'' of these structures
% is composed of a label (such as {\sc Theorem} or {\sc Remark})
% and a number which serializes an item in the sequence of items
% with the same label.
%
% Shortly after the introduction of \LaTeX{} at the Fachbereich
% Mathematik in Mainz, the desire to manipulate the layout of
% ``theorems'' arose.  In Mainz, the following two conventions came
% into general use:
% \begin{enumerate}
%   \item The number of the theorem is shown in the margin.
%   \item There is a line break at 
%         the end of the theorem header.
% \end{enumerate}
%
% Additionally, some journals require different formats which depend on
% the ``sort of theorem'': e.g.\ often remarks and definitions are set
% in |\rm|, while |\it| is employed for main theorems.
%
% Confronted with these requirements, a theorem environment was
% developed in Mainz which allows separate determination of the
% layout of the ``theorems sets'', comparable to |\pagestyle|.
%
%
% \section{The user interface}
% \subsection{Defining new theorem sets}
%
% \DescribeMacro\newtheorem
% As in the original \LaTeX{} version, the command |\newtheorem|
% defines a new ``theorem set'' or ``theorem-like structure''.
% Two required arguments name the new environment and give the text
% to be typeset with each instance of the new ``set'', while
% an optional argument determines how
% the ``set'' is enumerated:
% \begin{description}
%    \item[\tt \bslash newtheorem\{foo\}\{bar\}]
%       The theorem set {\envfont foo} (whose name is {\tt bar})
%       uses its own counter.
%    \item[\tt \bslash newtheorem\{foo2\}{[foo]}\{bar2\}]
%       The theorem set {\envfont foo2} (printed name {\tt bar2})
%       uses the same counter as the theorem set {\tt foo}.
%    \item[\tt \bslash newtheorem\{foo3\}\{bar3\}{[section]}] 
%       The theorem set {\envfont foo3} (printed name {\tt bar3}) is
%       enumerated within the counter {\tt section}, i.e.\ with every
%       new |\section| the enumeration begins again with 1, and
%       the enumeration is composed from the section-number and the
%       theorem counter itself.
% \end{description}
%
% \DescribeMacro\theoremstyle
% Additionally, the command |\theoremstyle| can define the layout
% of various, or all, theorem sets.  It should be noted that any
% theorem set defined by |\newtheorem| is typeset in the
% |\theoremstyle| that is current at the time of the definition.
% Thus, the following
% \begin{verbatim}
%    \theoremstyle{break}        \newtheorem{Cor}{Corollary}
%    \theoremstyle{plain}        \newtheorem{Exa}{Example}[section]
%\end{verbatim}                             ^^A No blank at line start
% leads to the result that the set {\envfont Cor} is formatted in the style
% {\tt break}, while the set {\envfont Exa} and all the following ones are
% formatted in the style {\tt plain}, unless another |\theoremstyle|
% follows.  Since the definitions installed by |\newtheorem| are
% global, one also can limit |\theoremstyle| locally by grouping
% braces.
%
% \DescribeMacro\theorembodyfont
% The choice of the font for the theorem body is completely
% independent of the chosen |\theoremstyle|; this has proven to
% be very advantageous.  For example,
% \begin{verbatim}
%   {\theorembodyfont{\rm}          \newtheorem{Rem}{Remark}}
%\end{verbatim}
% defines a theorem set {\envfont Rem}, which will be set
% in |\rm| in the current layout (which in our example is {\tt plain}).
% As with |\theoremstyle|, the |\theorembodyfont| chosen
% is that current at the time of |\newtheorem|.  If
% |\theorembodyfont| is not specified or one defines
% |\theorembodyfont{}|, then the font used will be that defined by
% the |\theoremstyle|.
%
% \DescribeMacro\theoremheaderfont It is also possible to customize
% the font used for the theorem headers.  This is, however, a global
% declaration, and therefore there should be at most one
% |\theoremheaderfont| declaration in the preamble.\footnote{If
% it is actually necessary to have different header fonts, one has to
% define new theorem styles (substituting the desired font) or specify
% the information directly in the {\tt\bslash newtheorem} declaration
% (the unclean variant).}
%
% \DescribeMacro\theorempreskipamount
% \DescribeMacro\theorempostskipamount
% Two additional parameters affect the vertical space around the
% theorem environments: |\theorempreskipamount| and
% |\theorempostskipamount| define, respectively, the spacing
% before and after such an environment.  These parameters apply for
% all theorem sets and can be manipulated with the ordinary length
% macros.  They are rubber lengths, (`{\sf skips}'), and therefore can
% contain {\tt plus} and {\tt minus} parts.
%
% Since the definition of theorem sets should---most sensibly---be
% placed in the preamble, we only allow installation there.
% It is therefore possible to release the memory used here after
% |\begin{document}|, in order to make room for other
% applications.
%
%
% \subsection{Existing theorem styles}
%
% The following theorem styles exist to date:
% \begin{deflist}{marginbreak}
%    \item[plain]
%       This theorem style emulates the original \LaTeX{} definition,
%       except that additionally the parameters
%       |\theorem...skipamount| are used.
%    \item[break]
%       In this style, the theorem header is followed by a line
%       break.
%    \item[marginbreak]
%       The theorem number is set in the margin, and there is a line
%       break as in {\tt break}.
%    \item[changebreak]
%       Like {\tt break}, but with header number and text interchanged.
%    \item[change]
%       Header number and text are interchanged, without a line break.
%    \item[margin]
%       The number is set in the left margin, without a line break.
% \end{deflist}
% All styles (except {\tt plain}) select |\sl| as the default
% |\theorembodyfont|.
% 
%
% \subsection{Examples}
%
% Given the above theorem sets {\envfont Cor}, {\envfont Exa}
% and {\envfont Rem},
% suppose that the preamble also contains the declarations:
% \begin{verbatim}
%    \theoremstyle{marginbreak}   \newtheorem{Lem}[Cor]{Lemma}
%    \theoremstyle{change}
%    \theorembodyfont{\it}        \newtheorem{Def}[Cor]{Definition}
%
%    \theoremheaderfont{\sc}
%\end{verbatim}
% Then the following are some typical examples of the typeset output
% resulting from their use.
%
% \begin{Cor}
%    This is a sentence typeset in the theorem environment {\envfont Cor}.
% \end{Cor}
%
% \begin{Exa}
%    This is a sentence typeset in the theorem environment {\envfont Exa}.
% \end{Exa}
%
% \begin{Rem}
%    This is a sentence typeset in the theorem environment {\envfont Rem}.
% \end{Rem}
%
% \begin{Lem}[Ben User]
%    This is a sentence typeset in the theorem environment {\envfont Lem}.
% \end{Lem}
%
% \begin{Def}[Very impressive Definition]
%    This is a sentence typeset in the theorem environment {\envfont Def}.
% \end{Def}
%
% The last two examples show the effect of the optional argument to
% a theorem environment (it is the text typeset in parentheses).
%
%
% \section{Special Considerations}
% \label{sec:newfonts}
%
% Theoremheader and body are implemented as a unit. This means that
% the |\theoremheaderfont|  will inherit characteristics of the
% |\theorembodyfont| if the new font selection scheme
% \cite{fs-latex} is in force. Thus, if for example
% |\theorembodyfont| is |\it| and |\theoremheaderfont|
% is |\bf| the font selected for the header will have the
% characteristics `bold extended italic'. If this is not desired one
% should set the |\theoremheaderfont| to something like
% \begin{verbatim}
%      \theoremheaderfont{\normalshape\bf}
%\end{verbatim}
% i.e.\ supplying all necessary font informations explicitly.
%
%
%
% \section{Acknowledgements}
%
% The publication of this set of macros was only possible with the
% help of Christina Busse (translating the manuscript into English),
% Joachim Pense (playing the r\^ole of typist), Chris Rowley
% (looking everything over) and many others providing useful
% suggestions.  
%
% \StopEventually{%
%    \begin{thebibliography}{9}
%       \bibitem{latex:source} {\sc Lamport, Leslie.} \newblock
%                               {\tt latex.tex}, version 2.09, date 
%                               Feb. 1990.  
%       \bibitem{fs-basics} {\sc Mittelbach, Frank} and
%                          {\sc Sch\"opf, Rainer.} \newblock
%                          A new font selection scheme for \TeX{}
%                          macro packages---the basic macros,
%                          \newblock
%                          \TUB 10\#2, pp.222--238  ,1989 
%       \bibitem{fs-latex} {\sc Mittelbach, Frank} and
%                          {\sc Sch\"opf, Rainer.} \newblock
%                          The \LaTeX{} interface for the new font
%                          selection scheme, 
%                          \newblock
%                          \TUB 11\#1, to appear.
%    \end{thebibliography}
%    \PrintIndex
%    \PrintChanges}
% 
% \section{Definition of the Macros}
%
% If the file has been loaded before, we abort immediately. If not,
% the current version of the style is shown on the screen and in the
% transcript file.
% \changes{v2.0e}{89/07/19}{Spaces removed from `typeout'.}
%    \begin{macrocode}
%<*style>
\@ifundefined{theorem@style}{}{\endinput}
\typeout{Style option: `theorem' \fileversion \space\space
         <\filedate>  (FMi)}
\typeout{English documentation as of \space\space\space
         <\docdate>  (FMi)}
%    \end{macrocode}
%
%
% \subsection{Definition of theorem styles and fonts}
%
% All the definitions in this file are done globally to allow
% inputting this file inside a group.
%
% \begin{macro}{\theoremstyle}
%    Before a theorem style can be installed, the
%    chosen style must be known. For that reason, we must test to see that
%    |\th@|\meta{style} is known or, more precisely, that
%    it is different from |\relax|. If the style is not known then
%    |\th@plain| is used.
%    \begin{macrocode}
\gdef\theoremstyle#1{%
   \@ifundefined{th@#1}{\@warning
          {Unknown theoremstyle `#1'. Using `plain'}%
          \theorem@style{plain}}%
%    \end{macrocode}
%    We save the theorem style to be used in the token register
%    |\theorem@style|.
%    \begin{macrocode}
      {\theorem@style{#1}}%
%    \end{macrocode}
%    Now we ``evaluate'' the theorem style: this means, we call the
%    macro |\th@|\meta{style} which will activate the relevant
%    definitions which are contained in a separate file.  This is done
%    in a group to suppress changes to the current font.  This could
%    otherwise pose problems together with the new font selection
%    scheme\footnote{When I printed the original article using the new
%    font selection scheme I ended with a document with slanted
%    typefaces (text headings and all) simply because one of the
%    theorem styles used {\tt\bslash sl} at toplevel.} if the
%    |\th@|\meta{style} is evaluated a second time.
% \changes{v2.1a}{90/02/15}{Group added around `th@..}
% \changes{v2.1a}{90/02/15}{Reseting of `..@begintheorem removed.}
%    \begin{macrocode}
      \begingroup
        \csname th@\the\theorem@style \endcsname
      \endgroup}
%    \end{macrocode}
% \end{macro}
%
%
% \begin{macro}{\@begintheorem}
% \changes{v2.1a}{90/02/15}{Relaxed at toplevel.}
% \begin{macro}{\@opargbegintheorem}
% \changes{v2.1a}{90/02/15}{Relaxed at toplevel.}
%    We reset |\@begintheorem| and |\@opargbegintheorem| to
%    |\relax| since these commands are no longer necessary at
%    toplevel. This will save a few tokens.
%    \begin{macrocode}
\global\let\@begintheorem\relax
\global\let\@opargbegintheorem\relax
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\theorem@style}
%    Obviously the {\sf token} register used above has to be
%    allocated. To assure the utmost compatibility with the
%    original \LaTeX{} definition, we set the default theorem style to
%    {\tt plain}, which implements the usual \LaTeX{} convention.
% \changes{v2.0f}{89/07/20}{Unnecessary `global' removed.}
%    \begin{macrocode}
\newtoks\theorem@style
\global\theorem@style{plain}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\theorembodyfont}
% \begin{macro}{\theorem@bodyfont}
%    If the |\theorembodyfont| is set by the user then it should not
%    interact with the default font set in the theorem style. When the
%    new font selection is in force this may happen if, for example,
%    the default is |\it| and the new |\theorembodyfont| is |\sf|. So
%    we add a |\reset@font| command in front of the user definition.
% \changes{v2.0f}{89/07/20}{Unnecessary `global' removed.}
% \changes{v2.0g}{89/09/19}{`theoremfont to `theorembodyfont.}
% \changes{v2.1c}{92/06/22}{`reset@font added and logic changed.}
%    \begin{macrocode}
\gdef\theorembodyfont#1{\theorem@bodyfont{\reset@font#1}}
\newtoks\theorem@bodyfont
\global\theorem@bodyfont{}
%    \end{macrocode}
% \end{macro}
% \end{macro}
% 
%
% \begin{macro}{\theoremheaderfont}
% \changes{v2.0g}{89/09/19}{Macro added.}
%    The font for the theorem headers is handled differently because
%    this definition applies to all theorem styles.
%    \begin{macrocode}
\gdef\theoremheaderfont#1{\gdef\theorem@headerfont{#1}%
%    \end{macrocode}
%    After using the macro once it is redefined to produce an error
%    message.
%    \begin{macrocode}
       \gdef\theoremheaderfont##1{%
        \typeout{\string\theoremheaderfont\space should be used
                 only once.}}}
%    \end{macrocode}
% \end{macro}
% 
% \begin{macro}{\theorem@headerfont}
% \changes{v2.0g}{89/09/19}{Macro added.}
%    To set the |\theorem@headerfont| default we first test if
%    the new fontselection scheme is in force.
% \changes{v2.1a}{90/02/15}{Support for new font selection.}
%    \begin{macrocode}
\ifx\normalshape\undefined
%    \end{macrocode}
%    If not we define it to expand into |\bf|. We don't use
%    |\let| just in case a following style option redefines this
%    macro.
%    \begin{macrocode}
\gdef\theorem@headerfont{\bf}
%    \end{macrocode}
%    Otherwise we reset the current shape before calling |\bf|. 
%    \begin{macrocode}
\else \gdef\theorem@headerfont{\normalshape\bf}\fi
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\th@plain}
% \begin{macro}{\th@break}
% \begin{macro}{\th@marginbreak}
% \begin{macro}{\th@changebreak}
% \begin{macro}{\th@change}
% \begin{macro}{\th@margin}
%    The different styles are defined in macros such as
%    |\th@plain|.  Since memory space is precious in
%    ``non-Big-versions'', we have to avoid offering too many unused
%    definitions.  Therefore we define these styles in separate files
%    that can be loaded on demand.  Thus the commands themselves only
%    load these files.
%    \begin{macrocode}
\gdef\th@plain{\input thp.sty}
\gdef\th@break{\input thb.sty}
\gdef\th@marginbreak{\input thmb.sty}
\gdef\th@changebreak{\input thcb.sty}
\gdef\th@change{\input thc.sty}
\gdef\th@margin{\input thm.sty}
%    \end{macrocode}
%    This list will be expanded when new styles become
%    available.  For testing,  just append new theorem substyles
%    as document options.
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
%
%
%
% \subsection{Definition of a new theorem set}
%
% As already pointed out, a new theorem environment can be defined in
% three different ways:
% \begin{verbatim}
%    \newtheorem{Lem}{Lemma}
%    \newtheorem{Lem}{Lemma}[section]
%    \newtheorem{Lem}[Theorem]{Lemma}
%\end{verbatim}
% The function of the macro |\newtheorem| is to recognize these
% cases and then to branch into one of the three macros
% |\@ynthm|, |\@xnthm| or |\@othm|.  This mechanism
% is adopted unchanged from \cite{latex:source}; the essential point
% here is that, for example, in the second case, the arguments {\tt
% Lem}, {\tt Lemma} and {\tt section} are passed over to the macro
% |\@xnthm|.
%
% We inspect this case first because the others present fewer problems,
% and thus are easily derived from this one.
%
% \begin{macro}{\@xnthm}
%    For our example arguments, the macro |\@xnthm| must fulfill
%    the following:
%    \begin{itemize}
%       \item
%          Define a new \LaTeX-counter `Lem'
%       \item
%          reset this counter within a |\section|
%       \item
%          define the macro |\theLem|
%       \item
%          define the environment macros |\Lem| and
%          |\endLem| using the current
%          |\theoremstyle| and |\theorem@bodyfont|.
%    \end{itemize}
%    Obviously, all this should happen only if the first argument
%    of |\@xnthm| (i.e.\ {\tt Lem} in our example) is chosen so
%    as not to conflict with any previously defined commands or
%    environments.  This test is performed by the \LaTeX{} macro
%    |\@ifdefinable|.
%    \begin{macrocode}
\gdef\@xnthm#1#2[#3]{\expandafter\@ifdefinable\csname #1\endcsname
%    \end{macrocode}
%    Therefore, the first argument of |\@ifdefinable| is the
%    expansion (in the example, |\Lem|) of
%    |\csname||#1\endcsname|.  The second argument is
%    executed only if the test has been completed successfully.
%    \begin{macrocode}
   {%
%    \end{macrocode}
%    Now we define the new counter. The names of the \LaTeX{}
%    macros employed should speak for themselves:
%    \begin{macrocode}
    \@definecounter{#1}\@addtoreset{#1}{#3}%
%    \end{macrocode}
%    In defining `|\theLem|' we must generate the desired macro
%    name by use of |\expandafter| and |\csname|.
%    \begin{macrocode}
    \expandafter\xdef\csname the#1\endcsname
%    \end{macrocode}
%    An |\xdef| is used in order to make the definition global,
%    and to ensure that it contains the replacement texts of
%    |\@thmcountersep| and |\@thmcounter|.\footnote{These
%    two macros can be defined by the document style.  Their default
%    values produce a `{\tt.}' as separation and an arabic
%    representation of the number.} However, not everything should be
%    expanded. For example, it saves space to use |\thesection|
%    instead of its---at times---lengthy expansion.
%    \begin{macrocode}
      {\expandafter \noexpand \csname the#3\endcsname
       \@thmcountersep \@thmcounter{#1}}%
%    \end{macrocode}
%    Thus with the defaults of \LaTeX{}, |\theLem| would be
%    replaced by the command sequence |\thesection.\arabic{Lem}|.
%
%    We will now look at the definition of the macro which is executed
%    at the beginning of the actual environment (in our example this
%    macro is |\Lem|). It should be noted that we use an
%    ``|\expandafter| trick'' to expand only certain parts of the
%    replacement text at the time of the definition.
%    \begin{macrocode}
    \def\@tempa{\global\@namedef{#1}}%
    \expandafter \@tempa \expandafter{%
%    \end{macrocode}
%    First, the macro that contains the current definitions of
%    |\@begintheorem| and |\@opargtheorem| should be called
%    up.  The name of this macro---as is already known---has the form
%    |\th@|\meta{theorem\ style}; therefore, it must be called by
%    \begin{macrocode}
      \csname th@\the \theorem@style
%    \end{macrocode}
%    In addition the default theorem font should be changeable, i.e.\
%    we have to insert the contents of |\theorem@bodyfont|. For
%    that reason, we expand even further, beyond |\endcsname|,
%    and thus insert the contents of the {\sf token} register
%    |\theorem@bodyfont| in the replacement text.
%    \begin{macrocode}
            \expandafter \endcsname \the \theorem@bodyfont
%    \end{macrocode}
%    Now it is time to call the macro |\@thm| which takes over
%    the further processing.  It has two arguments: the current
%    counter name (in our example, {\tt Lem}), and the text of the
%    label (in our example, {\tt Lemma}).
%    \begin{macrocode}
     \@thm{#1}{#2}}%
%    \end{macrocode}
%    With this, the `sub-definition' is complete.  The macro
%    |\@endtheorem| ends a theorem environment and is, so far,
%    nothing but an |\endtrivlist|.  (Hence it is defined
%    globally, and not within the theorem
%    styles.\footnote{This has to be changed as soon as theorem
%                     styles that
%                     change {\tt \bslash @endtheorem} exist.
%                     In such a case, all existing styles must be changed
%                     as well since they will have to reset the macro.})
%    Therefore, we can set it equivalent to the macro that ends the
%    theorem set (in our example, |\endLem|).  However, if some
%    day theorem styles exist that do change
%    |\@endtheorem|, we would have to use the commented-out line
%    instead.
%    \begin{macrocode}
    \global \expandafter \let \csname end#1\endcsname \@endtheorem
%   \global\@namedef{end#1}{\@endtheorem}%
%    \end{macrocode}
%    With these commands all the required definitions are employed,
%    unless the test |\@ifdefinable| has failed.  Therefore, we
%    end the second argument of this macro and with it the definition
%    of |\@xnthm|.
%    \begin{macrocode}
   }}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@ynthm}
%    The definition of |\@ynthm| is completely analogous. In
%    this case the new counter that is defined is not reset within
%    another counter; thus the definition of |\the...|
%    is simplified:
%    \begin{macrocode}
\gdef\@ynthm#1#2{\expandafter\@ifdefinable\csname #1\endcsname
   {\@definecounter{#1}%
    \expandafter\xdef\csname the#1\endcsname{\@thmcounter{#1}}%
%    \end{macrocode}
%    The rest of the definition corresponds literally to that of
%    |\@xnthm|:
%    \begin{macrocode}
    \def\@tempa{\global\@namedef{#1}}\expandafter \@tempa
     \expandafter{\csname th@\the \theorem@style \expandafter
     \endcsname \the\theorem@bodyfont \@thm{#1}{#2}}%
    \global \expandafter \let \csname end#1\endcsname \@endtheorem}}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@othm}
%    The definition of |\@othm| does not contain anything new. We
%    do not define a new counter but instead use one that has already
%    been defined.  Thus the only definition we need is that of this
%    pseudo-counter (i.e.\ |\the|\meta{env.\ name}).
%    \begin{macrocode}
\gdef\@othm#1[#2]#3{\expandafter\@ifdefinable\csname #1\endcsname
  {\expandafter \xdef \csname the#1\endcsname
     {\expandafter \noexpand \csname the#2\endcsname}%
%    \end{macrocode}
%    All other parts of the definition can be adopted from
%    |\@xnthm|. We have to remember, though, that in this case
%    the name of the current counter and the theorem label have moved
%    to the second and third arguments.
%    \begin{macrocode}
    \def\@tempa{\global\@namedef{#1}}\expandafter \@tempa
     \expandafter{\csname th@\the \theorem@style \expandafter
     \endcsname \the\theorem@bodyfont \@thm{#2}{#3}}%
    \global \expandafter \let \csname end#1\endcsname \@endtheorem}}
%    \end{macrocode}
% \end{macro}
%
% \subsection{Macros that are employed in a {\envfont theorem} environment}
%
% \begin{macro}{\@thm}
%    The macro |\@thm| has to increase the current counter.
%    Then, depending on whether the environment has (or does not have) an
%    optional argument, it has to branch into either
%    |\@begintheorem| or |\@opargtheorem|.
%    \begin{macrocode}
\gdef\@thm#1#2{\refstepcounter{#1}%
%    \end{macrocode}
%    Now we start a {\envfont trivlist} environment, and give
%    |\@topsep| and |\@topsepadd| the values of the {\sf
%    skip} registers |\theorempreskipamount| and
%    |\theorempostskipamount|. The value in |\@topsep| is
%    the vertical space that is inserted by the first (and only)
%    |\item| in our |\trivlist| whilst |\@topsepadd| is
%    inserted by |\@endparenv| at the end of that {\envfont trivlist}
%    environment.  By using these registers, we obtain the desired
%    space around a {\envfont theorem} environment.
%    \begin{macrocode}
   \trivlist
   \@topsep \theorempreskipamount               % used by first \item
   \@topsepadd \theorempostskipamount           % used by \@endparenv
%    \end{macrocode}
%    Now we have to test whether an optional argument has been given.
% \changes{v2.0d}{89/07/18}{Forgotten percent added.}
%    \begin{macrocode}
   \@ifnextchar [%
%    \end{macrocode}
%    If there is an optional argument, we will call |\@ythm|, and
%    move the arguments read back into the input stream.
%    \begin{macrocode}
   {\@ythm{#1}{#2}}%
%    \end{macrocode}
%    If not, we call |\@begintheorem|. Its first argument is the
%    name of the theorem set (hence the second argument of
%    |\@thm|). Its second argument is the macro that produces the
%    current number.
%    \begin{macrocode}
   {\@begintheorem{#2}{\csname the#1\endcsname}\ignorespaces}}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@xthm}
% \begin{macro}{\@ythm}
%    Both these macros were originally called by |\@thm|.  We do
%    not need |\@xthm| anymore, hence we reset it to
%    |\relax|. The definition of |\@ythm| has not changed at
%    all from its definition in \LaTeX. In order to make the macros
%    easier to understand, we will
%    nevertheless present it (commented out).
%    \begin{macrocode}
\global\let\@xthm\relax
% \def\@ythm#1#2[#3]{\@opargbegintheorem{#2}{\csname
%           the#1\endcsname}{#3}\ignorespaces}
%    \end{macrocode}
%    The primitive |\ignorespaces| in |\@ythm| and
%    |\@thm| is needed to remove the spaces between the
%    |\begin{...}| and the actual text.
% \end{macro}
% \end{macro}
%
%
% \subsection{Definition of the theorem substyles}
% 
% As already pointed out, the theorem substyles, defined below, are
% only loaded when necessary.  Note that all these substyles, except
% {\tt plain}, have |\sl| as the default body font.
%
% \subsubsection{The {\tt plain} style}
% \input{thp.doc}
%
% \subsubsection{The {\tt break} style}
% \input{thb.doc}
%
% \subsubsection{The {\tt changebreak} style}
% \input{thcb.doc}
%
% \subsubsection{The {\tt change} style}
% \input{thc.doc}
%
% \subsubsection{The {\tt marginbreak} style}
% \input{thmb.doc}
%
% \subsubsection{The {\tt margin} style}
% \input{thm.doc}
%
%
% \subsection{Final Definitions}
%
% \begin{macro}{\theorempreskipamount}
% \begin{macro}{\theorempostskipamount}
%    The {\sf skip} parameters that regulate the vertical empty space
%    before and after the {\envfont theorem} environment have 
%    to be allocated as well.
% \changes{v2.0f}{89/07/20}{Unnecessary `global' removed.}
%    \begin{macrocode}
\newskip\theorempreskipamount
\newskip\theorempostskipamount
%    \end{macrocode}
%    Since we have used the same values for all theorem sets, we now can
%    assign them.
%    \begin{macrocode}
\global\setlength\theorempreskipamount{12pt plus 5pt minus 3pt}
\global\setlength\theorempostskipamount{8pt plus 3pt minus 1.5pt}
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
%
% \begin{macro}{\@endtheorem}
%    The same holds for the macro |\@endtheorem|, which ends a
%    {\envfont theorem} environment. Since it is the same for all theorem sets,
%    it is removed from the macros |\th@|\meta{style}.  It simply
%    ends the {\envfont trivlist} environment, which was begun in
%    |\@thm|.
%    \begin{macrocode}
\global\let\@endtheorem=\endtrivlist
%    \end{macrocode}
% \end{macro}
%
%
%
% \begin{macro}{\@preamblecmds}
%    All macros defined above are to be used only in the preamble.
%    Therefore, we insert them in |\@preamblecmds| (separated by
%    the macro |\do|). All the commands not allowed after the
%    |\begin{document}| are stored here. This is achieved by
%    having |\document| (with the help of |\do|) redefine
%    all macros in |\@preamblecmds| to a \LaTeX{} error routine
%    call.
% \changes{v2.0g}{89/09/19}{`theoremheaderfont and `theorembodyfont added.}
%    \begin{macrocode}
{\def\do{\noexpand\do\noexpand}
\xdef\@preamblecmds{\@preamblecmds \do\@xnthm \do\@ynthm \do\@othm
        \do\newtheorem \do\theoremstyle \do\theorembodyfont
        \do\theoremheaderfont}
}
%    \end{macrocode}
% \end{macro}
%
% Finally we declare the {\tt plain} theorem style to be the default.
% \changes{v2.1b}{90/06/04}{Fixed missing `item by declaring default style.}
%    \begin{macrocode}
\theoremstyle{plain}
%</style>
%    \end{macrocode}
%
%
% \section{The documentation driver file}
%
% The next bit of code contains the documentation driver file for
% \TeX{}, i.e., the file that will produce the documentation you are
% currently reading. It will be extracted from this file by the {\tt
% docstrip} program.
%
% The sub style options are loaded to test for simple typos in the
% macros.
%
%    \begin{macrocode}
%<+drv>\documentstyle[theorem,thb,thp,thmb,thc,thm,thcb%
%<+drv>              ,doc%
%<+drv>              ]{article}
%<+drv>
%<+drv>%%   The next few lines define theorem sets which are used
%<+drv>%%   in the example section of the documentation.
%<+drv>
%<+drv> \theoremstyle{break}      \newtheorem{Cor}{Corollary}
%<+drv> \theoremstyle{plain}      \newtheorem{Exa}{Example}[section]
%<+drv> {\theorembodyfont{\rm}    \newtheorem{Rem}{Remark}}
%<+drv> \theoremstyle{marginbreak}\newtheorem{Lem}[Cor]{Lemma}
%<+drv> \theoremstyle{change}
%<+drv> \theorembodyfont{\it}     \newtheorem{Def}[Cor]{Definition}
%<+drv>
%<+drv>\theoremheaderfont{\sc}
%<+drv>
%<+drv>\CodelineIndex
%<+drv>\RecordChanges
%<+drv>
%<+drv>
%<+drv>\begin{document}
%<+drv>   \DocInput{theorem.doc}
%<+drv>\end{document}
%    \end{macrocode}
%
%
% \Finale

\endinput