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+%%% ====================================================================
+%%%  @LaTeX-doc-source-file{
+%%%     filename        = "snapshot.dtx",
+%%%     version         = "1.14",
+%%%     date            = "2002/03/05",
+%%%     time            = "15:29:00 EST",
+%%%     checksum        = "39090 807 3449 29761",
+%%%     author          = "American Mathematical Society",
+%%%     copyright       = "Copyright 2001 American Mathematical Society,
+%%%                        all rights reserved.  Copying of this file is
+%%%                        authorized only if either:
+%%%                        (1) you make absolutely no changes to your copy,
+%%%                        including name; OR
+%%%                        (2) if you do make changes, you first rename it
+%%%                        to some other name.",
+%%%     address         = "American Mathematical Society,
+%%%                        Electronic Products and Services,
+%%%                        PO Box 6248,
+%%%                        Providence, RI 02940,
+%%%                        USA",
+%%%     email           = "tech-support@ams.org",
+%%%     URL             = "http://www.ams.org/",
+%%%     supported       = "yes",
+%%%     keywords        = "version, compatibility, dependencies, LaTeX",
+%%%     abstract        = "This package provides a way for a LaTeX
+%%%                        document to specify, for each external file
+%%%                        on which the document depends, which version
+%%%                        is required to guarantee output fidelity.",
+%%%     docstring       = "The checksum field above contains a CRC-16
+%%%                        checksum as the first value, followed by the
+%%%                        equivalent of the standard UNIX wc (word
+%%%                        count) utility output of lines, words, and
+%%%                        characters.  This is produced by Robert
+%%%                        Solovay's checksum utility.",
+%%%  }
+%%% ====================================================================
+% \iffalse
+%<*driver>
+\NeedsTeXFormat{LaTeX2e}
+\documentclass{amsdtx}
+\providecommand{\qq}[1]{\textquotedblleft#1\textquotedblright}
+\providecommand{\mdash}{\textemdash}
+\begin{document}
+\title{The \pkg{snapshot} package}
+\author{American Mathematical Society\\Michael Downes}
+\date{Version \fileversion, \filedate}
+\hDocInput{snapshot.dtx}
+\end{document}
+%</driver>
+% \fi
+%
+% \MakeShortVerb{\|}
+%
+% \maketitle
+% \section{Introduction}
+%
+%    The \pkg{snapshot} package helps the owner of a \LaTeX{} document
+%    obtain a list of the external dependencies of the document, in a
+%    form that can be embedded at the top of the document. To put it
+%    another way, it provides a snapshot of the current processing
+%    context of the document, insofar as it can be determined from
+%    inside \LaTeX{}.
+%
+%    If a document contains such a dependency list, then it becomes
+%    possible to arrange that the document be processed always with the
+%    same versions of everything, in order to ensure the same output.
+%    This could be useful for someone wanting to keep a \LaTeX{}
+%    document on hand and consistently reproduce an identical DVI file
+%    from it, on the fly; or for someone wanting to shield a document
+%    during the final stages of its production cycle from unexpected
+%    side effects of routine upgrades to the \TeX{} system.
+%
+%    Normal usage of the \pkg{snapshot} package involves the following
+%    steps:
+% \begin{enumerate}
+%    \item Add a \cn{RequirePackage} statement at the top of the
+%    document:
+% \begin{verbatim}
+%      \RequirePackage{snapshot}
+%      \documentclass{article}
+%        ...
+% \end{verbatim}
+%
+%    \item Run \latex/ on the document. This will produce a dependency
+%    list in a file \verb'\jobname.dep'.
+%
+%    \item Insert the \fn{.dep} file at the top of the document, before
+%    \cn{documentclass}. The following example shows what you would end
+%    up with for a document that used the article documentclass and the
+%    graphicx package:
+% \begin{verbatim}
+%  \RequirePackage{snapshot}[1999/11/03]
+%  \RequireVersions{
+%    *{application}{TeX}     {1990/03/25 v3.x}
+%    *{format} {LaTeX2e}     {1999/06/01 v2.e}
+%    *{package}{snapshot}    {1999/11/03 v1.03}
+%    *{class}  {article}     {1999/01/07 v1.4a}
+%    *{file}   {size10.clo}  {1999/01/07 v1.4a}
+%    *{package}{graphicx}    {1999/02/16 v1.0f}
+%    *{package}{keyval}      {1999/03/16 v1.13}
+%    *{package}{graphics}    {1999/02/16 v1.0l}
+%    *{package}{trig}        {1999/03/16 v1.09}
+%    *{file}   {graphics.cfg}{0000/00/00 v0.0}
+%    *{file}   {dvips.def}   {1999/02/16 v3.0i}
+%  }
+%  \documentclass{article}
+%  \usepackage{graphicx}
+%  ...
+% \end{verbatim}
+% \end{enumerate}
+%
+%    The package option \opt{log} will cause the dependency list to
+%    appear in the \latex/ log file instead of in a separate \fn{.dep}
+%    file:
+% \begin{verbatim}
+% \RequirePackage[log]{snapshot}
+% \end{verbatim}
+%
+%    Making the necessary arrangements to ensure that future \latex/
+%    runs of the document actually call in the specified versions is a
+%    separate problem. The \pkg{snapshot} package only provides a way to
+%    generate the dependency list. However, the \cn{RequireVersions}
+%    statement does record the given information in a form that can be
+%    accessed from within \latex/. (It is for this purpose that it is not
+%    simply a comment.) In principle a package could be set up so that a
+%    later version would automatically attempt to emulate an earlier
+%    version if an earlier version was specified\mdash much as \latex/
+%    currently switches to 2.09 compatibility mode if it sees
+%    \cn{documentstyle} instead of \cn{documentclass}.
+%
+%    For maximum reliability font checksums should also be reported in
+%    the dependency list, but standard \tex/ 3.x does not provide direct
+%    access to font checksums for macro programmers. This information
+%    could be added by a separate script that scans the DVI file.
+%
+%    When a graphics file is read in by a \latex/ document using the
+%    standard \cn{includegraphics} command, it gets a dummy version
+%    number string of
+%\begin{verbatim}
+%Graphics file (type foo)
+%\end{verbatim}
+%    where foo is typically \texttt{eps}. This is with the current
+%    version of the \pkg{graphics} package (at the time of this writing:
+%    1999/02/16 v1.0l). What this means in practice is that all graphics
+%    files will have their snapshot date and version number recorded as
+%\begin{verbatim}
+%Graphics v0.0
+%\end{verbatim}
+%    and will always compare equal (the string ``Graphics'' will be used
+%    in place of a date, but since comparison is done with \cs{ifx} it
+%    doesn't make any real difference).
+%
+%    It would be possible, for \fn{.eps} files at least, to read the
+%    CreationDate comment that is normally included in the file header
+%    and use that as the basis of comparison. Recording the bounding box
+%    numbers instead of a dummy version number would also be a possibly
+%    useful stratagem. But I have left these possibilities untouched for
+%    the time being [mjd,2001-05-14].
+%
+% \DescribeMacro{\RequireVersions} The \cn{RequireVersions} command
+%    scans its argument for file names and associated version number
+%    information. The syntax of a version line for a particular file is
+% \begin{quote}
+% \verb'*{' \emph{file type} \verb'}{' \emph{file name} \verb'}{'
+%    \emph{version info} \verb'}'
+% \end{quote}
+%    In other words, the \verb'*' character in this context is like a
+%    command that takes three arguments. The extension part of the
+%    file name should be omitted in the second argument, except when the
+%    file type is \fn{file} (following the conventions of \latex/'s
+%    \cn{ProvidesPackage} and \cn{ProvidesFile} commands). The most
+%    commonly used file types are as follows.
+% \begin{description}
+% \item[class] A \latex/ documentclass file.
+% \item[package] A \latex/ package file.
+% \item[tfm] A \tex/ font metric file. In this case the \qq{version
+%    number} is the checksum, and unless you are using an extended
+%    version of \tex/ this information is not accessible from inside
+%    \latex/, so it must be filled in by an outside process.
+%    By default, font metric files are not listed in the dependency list
+%    since the checksum info is not available. There is a package option
+%    \opt{tfm} to turn on the logging of metric files. (Not yet
+%    implemented [mjd,1999/09/23])
+%
+% \item[format] This is almost always \fn{LaTeX2e}. Other possibilities
+%    would be \fn{elatex} or \fn{lambda}. The information comes from
+%    \cs{fmtname}.
+% \item[application] This is usually \fn{TeX} with version number
+%    \fn{3.x}. From inside \latex/ there is no reliable way to get the
+%    exact version number (one could check to see if version 2.x is in
+%    use, but this is unlikely to be relevant, nowadays, so I have not
+%    bothered).
+% \item[file] None of the above: some other file of miscellaneous type,
+%    e.g., \fn{.clo}, \fn{.cfg}, \fn{.tex}, or \fn{.def}.
+% \end{description}
+%
+%    The \cn{RequireVersions} command can be given an optional
+%    \qq{ident} argument, similar to the argument of a \cn{label}
+%    command. This is not used internally but it could be used to
+%    assign a label to particular groups of files in case that helps
+%    with external processing.
+%
+% \section{Warning and error options}
+%
+%    If the \pkg{snapshot} package is invoked with the \opt{error}
+%    option \emph{and also} the document contains a \cn{RequireVersions}
+%    statement, then each subsequent \cn{ProvidesFile},
+%    \cn{ProvidesPackage}, and \cn{ProvidesClass} statement will compare
+%    date and version number information with the corresponding
+%    information from the \cn{RequireVersions} statement and give an
+%    error message if a mismatch is detected. With the \opt{warning}
+%    option you get warnings instead of errors. By default both the date
+%    and the version number are compared; this behavior can be modified,
+%    however, by giving additional options:
+% \begin{description}
+%   \item[date] compare only dates,
+%   \item[version] compare only version numbers,
+%   \item[major-version] use only the major version number when
+%    comparing.
+% \end{description}
+%
+%    \textbf{Note:} A file that doesn't have any sort of
+%    \cn{ProvidesFile} or \cn{ProvidesPackage} statement in it will show
+%    up in the dependency list, with a dummy date and version number of
+%    0000/00/00 v0.0, but there is no way, of course, to give any
+%    meaningful warning or error message about version mismatches for
+%    such a file.
+%
+% \StopEventually{}
+%
+% \section{Implementation}
+%    Standard declaration of package name and date.
+%    \begin{macrocode}
+\NeedsTeXFormat{LaTeX2e}[1994/12/01]
+\ProvidesPackage{snapshot}[2002/03/05 v1.14]
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+\let\@xp\expandafter \let\@nx\noexpand
+%    \end{macrocode}
+%
+%    Calling the \pkg{snapshot} package in a document causes \latex/ to
+%    list the file names and versions in the \tex/ log or in a \fn{.dep}
+%    file, so that the information may be easily copied into the
+%    document file. The list so generated is nothing more than a slight
+%    adaptation of the output from \latex/'s \cn{listfiles} command; it
+%    puts essentially the same information into a slightly more
+%    structured form so that it will be easier to use.
+%
+%    For the standard mechanisms that are already built into \latex/
+%    (e.g., the handling of the second optional argument of
+%    \cs{LoadClass}), the de facto \qq{version number} is the
+%    \emph{date} given in the optional argument of a \cn{ProvidesClass}
+%    or similar command. Even though most \cn{ProvidesWhatever} commands
+%    also give something that follows the usual form of version
+%    numbers\mdash a string of the form \verb'v2.3'\mdash this is only a
+%    convention, not used internally by \latex/, and the identification
+%    string of a random loaded file is not guaranteed to include it. The
+%    \pkg{snapshot} package copies both pieces of information if
+%    available; if the second piece is not present, a dummy number
+%    \verb'0.0' is supplied. Similarly, files that don't include any
+%    \cn{ProvidesWhatever} statement will get a dummy date of
+%    \verb'0000/00/00'; \tex/ system administrators who want to ensure
+%    maximal accuracy of the snapshot information should therefore make
+%    it a practice to use \cn{ProvidesFile} in \fn{.cfg} files and other
+%    local files that might have an impact on the output fidelity of
+%    their documents.
+%
+%  \begin{macro}{\RequireVersions}
+%
+%    Optional argument of \cn{RequireVersions} allows assigning a name to a
+%    particular collection of files. This might be useful for setting a
+%    \tex/ inputs path.
+%    \begin{macrocode}
+\newcommand{\RequireVersions}[2][]{%
+  \let\snap@check\snap@compare@versions
+  \let\snap@selfcheck\snap@selfcheck@a
+  \@ifnextchar *\snap@store@version\snap@store@error#2*{end}{}{}%
+}
+\@onlypreamble\RequireVersions
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+\def\snap@store@error#1{%
+  \PackageError{snapshot}{Expected '*' here, not '#1'}\@ehc
+}
+\@onlypreamble\snap@store@error
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+\def\snap@store@version #1#2#3#4{%
+  \@xp\snap@store@b\csname snapx@#2\endcsname{#2}{#3}{#4}%
+}
+\@onlypreamble\snap@store@version
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+\def\@fmtextension{fmt}
+\def\@tfmextension{tfm}
+\edef\snapx@package{.\@pkgextension}
+\edef\snapx@class{.\@clsextension}
+\edef\snapx@format{.\@fmtextension}
+\edef\snapx@tfm{.\@tfmextension}
+\long\def\snapx@application{}
+\let\snap@file=\@empty
+\let\snapx@end\@@end
+%    \end{macrocode}
+%
+%    For a package named \fn{foo.sty}, this function defines
+%    \cs{rqv@foo.sty} to hold the date and version information.
+%    \begin{macrocode}
+\def\snap@store@b#1#2#3#4{%
+  \ifx#1\snapx@end
+    \@xp\@gobblefour
+  \else
+    \ifx#1\relax \let#1\@empty\fi
+    \def\@tempa##1 ##2 ##3\@nil{##1 ##2}%
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+    \ifx#1\snapx@application
+    \else
+      \xdef\rqv@list{\rqv@list
+        \ifx\@empty\rqv@list\else,\fi
+        #3#1%
+      }%
+    \fi
+    \@xp\xdef\csname rqv@#3#1\endcsname{\@tempa#4 v?.? ? \relax\@nil}%
+    \ifx#1\snapx@format \snap@check{#3.fmt}%
+    \else \snap@selfcheck{#3.sty}%
+    \fi
+  \fi
+  \@ifnextchar *\snap@store@version\snap@store@error
+}
+\@onlypreamble\snap@store@b
+%    \end{macrocode}
+%  \end{macro}
+%
+%    Default setup is geared to write the dependency list to a \fn{.dep}
+%    file. The option \opt{log} means write it to the \tex/ log instead.
+%    \begin{macrocode}
+\def\snap@write{\immediate\write\snap@out}
+\let\snap@out\sixt@@n % fallback, probably never used
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+\DeclareOption{dep}{%
+  \def\snap@write{\immediate\write\snap@out}%
+}
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+\DeclareOption{log}{%
+  \let\snap@write\typeout
+}
+%    \end{macrocode}
+%
+%    The purpose of the `test' option is to support a separate testing
+%    procedure that resolves file names. If the \cs{RequireVersions}
+%    data is extracted to a separate file, and
+%\begin{verbatim}
+%\RequirePackage[test]{snapshot}
+%\end{verbatim}
+%    is added at the top, then the file can be run as a small separate
+%    \LaTeX{} job whose sole purpose is to produce in the log file a
+%    nice list of fully resolved file names. A limited, but
+%    system-independent variant of the \fn{kpsewhich} idea.
+%
+%    \begin{macrocode}
+\let\snap@fake@b\relax
+\DeclareOption{test}{%
+  \def\snap@fake@b{\endinput \futurelet\@let@token\snap@ignoline}%
+}
+%    \end{macrocode}
+%
+%    For each font used by a document, we would like to list the
+%    \fn{.tfm} file name and checksum. If \tex/ provided a
+%    \cn{fontchecksum} primitive similar to \cn{fontname} that could be
+%    used to get the checksum of any font, it would just about be
+%    feasible to do this entirely from within \latex/. As a partial
+%    solution we could at least generate the list of font file names, to
+%    make it easier for an external utility to add the checksums.
+%
+%    In practice, extracting font names and checksums from the \fn{.dvi}
+%    file will probably work well enough, leaving no work to be done by
+%    the \pkg{snapshot} package in this area. But theoretically speaking
+%    the output of a document could be affected by font metric files
+%    that are loaded during \latex/ processing but that do not show up
+%    in the \fn{.dvi} file.
+%    \begin{macrocode}
+\DeclareOption{tfm}{%
+  \typeout{Option 'tfm' not implemented yet [1999/09/23]}%
+}
+%    \end{macrocode}
+%
+%    Warnings and errors.
+%    \begin{macrocode}
+\def\snap@mismatch@warning#1#2#3{\PackageWarningNoLine{#1}{#2}}
+\def\snap@mismatch{\snap@mismatch@warning}
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+\DeclareOption{error}{%
+  \def\snap@mismatch{\PackageError}%
+  \ifx\snap@select\@empty \let\snap@select\snap@select@all \fi
+}
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+\DeclareOption{warning}{%
+  \def\snap@mismatch{\snap@mismatch@warning}%
+  \ifx\snap@select\@empty \let\snap@select\snap@select@all \fi
+}
+%    \end{macrocode}
+%
+%    Because the exact form of the version number is not mandated by
+%    LaTeX, just take the first two ``words'' delimited by spaces. And
+%    take a little extra care to properly handle multiple spaces between
+%    the words.
+%    \begin{macrocode}
+\def\snap@select@all#1#2 #3#4 #5\@nil{#1#2 #3#4}
+\let\snap@select\@empty
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+\DeclareOption{date}{%
+  \def\snap@select#1#2 #3\@nil{#1#2}%
+}
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+\def\snap@select@version#1{%
+  \ifodd 0#11 \@xp\snap@sva\@xp#1\else\@xp\snap@select@version\fi
+}
+\def\snap@sva#1.#2 #3\@nil{#1.#2}
+\def\snap@select@major#1{%
+  \ifodd 0#11 \@xp\snap@svm\@xp#1\else\@xp\snap@select@major\fi
+}
+\def\snap@svm#1.#2\@nil{#1}
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+\DeclareOption{version}{%
+  \def\snap@select#1#2 #3{\snap@select@version #3}%
+}
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+\DeclareOption{major-version}{%
+  \def\snap@select#1#2 #3{\snap@select@major #3}%
+}
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+\ProcessOptions\par
+%    \end{macrocode}
+%
+%    We need the following patch to make up for the fact that
+%    \cs{@pkgextension} and \cs{@clsextension} are marked in the \latex/
+%    kernel as \qq{only preamble}.
+%    \begin{macrocode}
+\edef\snap@restore@extensions{%
+  \def\@nx\@pkgextension{\@pkgextension}%
+  \def\@nx\@clsextension{\@clsextension}%
+}
+%    \end{macrocode}
+%
+%    Pad filename strings out to 8+3 length so that the list will look
+%    pretty.
+%    \begin{macrocode}
+\def\snap@pad#1#2#3#4#5#6#7#8#9{\snap@pad@a{#1#2#3#4#5#6#7#8#9}}
+\def\snap@pad@a#1#2#3#4#5\@nil{\snap@pad@b#1#2#3#4\space\@nil}
+\def\snap@pad@b#1\space#2\@nil#3{\def#3{#2}}
+%    \end{macrocode}
+%
+%    First stage: discard leading spaces before the first and second
+%    nonspace strings in the argument. Take the first nonspace string as
+%    the date. Since we only do equal/not-equal testing on dates, it
+%    does not seem essential to test if it is really a valid date string
+%    or not (yyyy/mm/dd).
+%    \begin{macrocode}
+\def\snap@trim@version#1#2 #3{#1#2 \snap@trim@b #3}
+%    \end{macrocode}
+%    Second stage: Scan for a version number. In order to handle some
+%    idiosyncratic cases, such as url.sty version 1.4, we can't simply
+%    take the second nonspace string as the version number but need to
+%    look for a leading digit.
+%    \begin{macrocode}
+\def\snap@trim@b#1{\ifodd 0#11 v#1\@xp\snap@trim@c\fi \snap@trim@b}
+%    \end{macrocode}
+%    Arg 1 here is \cs{snap@trim@b}, which we just need to discard.
+%    \begin{macrocode}
+\def\snap@trim@c#1#2 #3\@nil{#2}
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+\let\rqv@list=\@empty
+%    \end{macrocode}
+%
+%    If \verb'\fmtname.fmt' is not already in the file list, add it.
+%    \begin{macrocode}
+\edef\@tempc#1\fmtname{#1\fmtname}\@tempc
+\def\@tempa#1,\fmtname.fmt,#2#3\@nil{#2}
+\edef\@tempb{\@nx\@tempa,\@filelist,\fmtname.fmt,}
+\if ?\@tempb?\@nil
+  \edef\@filelist{\fmtname.fmt,\@filelist}%
+  \def\@tempc{LaTeX2e}%
+  \@xp\edef\csname ver@\fmtname.fmt\endcsname{%
+    \fmtversion\space
+    v\ifx\@tempc\fmtname 2.e\else ?.?\fi
+  }%
+\fi
+\listfiles
+\def\@dofilelist{%
+  \snap@restore@extensions
+  \ifx\rqv@list\@empty
+  \else \rqv@compare@lists
+  \fi
+  \ifx\snap@write\typeout
+  \else
+    \newwrite\snap@out
+    \immediate\openout\snap@out=\jobname.dep \relax
+  \fi
+  \snap@write{\string\RequireVersions\@charlb}%
+%    \end{macrocode}
+%    Since the exact version number of \TeX{} is not normally accessible
+%    from inside \latex/, we use a nominal date of 1990/03/25, which is
+%    when version 3.0 of \fn{tex.web} was released by Knuth.
+%    \begin{macrocode}
+  \snap@write{\space\space *{application}{TeX}%
+             \space\space\space\space\space{1990/03/25 v3.x}}%
+  \@for\@currname:=\@filelist\do{%
+    \filename@parse\@currname
+    \ifx\filename@ext\relax
+      \def\@tempa{file}\def\@tempd{.tex}\def\filename@ext{tex}%
+      \def\@tempb{~~~}%
+    \else\ifx\filename@ext\@pkgextension
+      \def\@tempa{package}\let\@tempd\@empty
+      \def\@tempb{}%
+    \else\ifx\filename@ext\@clsextension
+      \def\@tempa{class}\let\@tempd\@empty
+      \def\@tempb{~~}%
+    \else\ifx\filename@ext\@fmtextension
+      \def\@tempa{format}\let\@tempd\@empty
+      \def\@tempb{~}%
+    \else\ifx\filename@ext\@tfmextension
+      \def\@tempa{tfm}\let\@tempd\@empty
+      \def\@tempb{~~~~}%
+    \else
+      \def\@tempa{file}\edef\@tempd{.\filename@ext}%
+      \def\@tempb{~~~}%
+    \fi\fi\fi\fi\fi
+    \@xp\let\@xp\@tempe
+      \csname ver@\filename@base.\filename@ext\endcsname
+%    \end{macrocode}
+%    If a file contains just \verb'\ProvidesFoo{xyz}' without \emph{any}
+%    optional argument, then \cs{ver@xyz} ends up empty. Resetting it to
+%    \cs{relax} is the easiest way to get the fallback version
+%    number in that case also.
+%    \begin{macrocode}
+    \ifx\@tempe\@empty \let\@tempe\relax \fi
+    \edef\@tempe{%
+      \ifx\@tempe\relax 0000/00/00 v0.0%
+      \else
+        \@xp\@xp\@xp\snap@trim@version\@xp\@tempe\space v0.0 v0.0 \@nil
+      \fi
+    }%
+    \edef\@tempc{\filename@area\filename@base\@tempd}% full file name
+    \@xp\snap@pad\@tempc\space~~~~~~~~~~~~~~~~\@nil\@tempd
+    \begingroup \let~\space
+      \snap@write{\space\space *{\@tempa}\@tempb{\@tempc}\@tempd{\@tempe}}%
+    \endgroup
+  }%
+  \snap@write{\@charrb}%
+  \ifx\snap@write\typeout
+  \else \immediate\closeout\snap@out
+    \typeout{Dependency list written on \jobname.dep.}%
+  \fi
+}%
+%    \end{macrocode}
+%
+%    The \cs{rqv@compare@lists} function checks to see if any files
+%    are found only in the RequireVersions list or only in
+%    \cs{@filelist}. To see which files are only in \cs{@filelist}, we
+%    map the \cs{rqv@condense} function across both lists, reinitializing
+%    \cs{L} (used here as a scratch variable) in between. As a side
+%    effect this leaves the desired file names in \cs{L}. Then the same
+%    process with the order of the lists reversed tells us which ones
+%    are only in \cs{rqv@list}.
+%    \begin{macrocode}
+\def\rqv@condense#1,{%
+  \if ,#1,%
+  \else
+    \@xp\ifx\csname ver@#1\endcsname\N
+    \else
+      \edef\L{\L,#1}%
+      \@xp\let\csname ver@#1\endcsname=\N
+    \fi
+  \fi
+  \rqv@condense
+}
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+\def\rqv@compare@lists{%
+  \begingroup
+  \def\N{1}\let\L=\@gobble
+  \@xp\rqv@condense \rqv@list,TeX,{,\relax\@xp\@gobbletwo\@xp},%
+  \ifx\L\@gobble\let\L\@empty\fi
+  \let\rqv@list=\L
+  \let\L=\@gobble
+  \@xp\rqv@condense \@filelist,{,\relax\@xp\@gobbletwo\@xp},%
+  \ifx\L\@gobble\let\L\@empty\fi
+  \@for\@currname:=\L\do{%
+    \snap@mismatch{snapshot}{^^J%
+      File \@currname\space loaded though not in
+      \noexpand\RequireVersions list%
+    }\@ehc
+  }%
+  \def\N{2}\let\L=\@gobble
+  \@xp\rqv@condense\@filelist,TeX,{,\relax\@xp\@gobbletwo\@xp},%
+  \let\L=\@gobble
+  \@xp\rqv@condense\rqv@list,{,\relax\@xp\@gobbletwo\@xp},%
+  \ifx\L\@gobble\let\L\@empty\fi
+  \@for\@currname:=\L\do{%
+    \snap@mismatch{snapshot}{^^J%
+      File \@currname\space [\csname rqv@\@currname\endcsname]
+      required but not loaded%
+    }\@ehc
+  }%
+  \endgroup
+}
+%    \end{macrocode}
+%
+%    See the documentation above for the `test' option.
+%    \begin{macrocode}
+\begingroup \catcode\endlinechar=12\relax %
+\long\gdef\snap@ignoline#1
+{}\endgroup %
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+\def\snap@fake@input#1#2#3#4{%
+  \ifx#1\snapx@end
+    \aftergroup\@@end \@xp\@gobblefour
+  \else
+    \ifx#1\snapx@format
+    \else
+      \message{^^J}%
+      \@xp\snap@fake@b\@@input #3#1\relax
+    \fi
+  \fi
+  \@ifnextchar *\snap@store@version\snap@store@error
+}
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+\newcommand{\rqvTest}[2][]{%
+  \begingroup \catcode\endlinechar=12
+  \catcode`\%=12 \catcode`\{=12 \catcode`\}=12\relax
+%    \end{macrocode}
+%    Since \cs{snap@fake@input} just compares \cs{snapx@foo} with
+%    \cs{ifx}, making \cs{snapx@application}
+%    and \cs{snapx@tfm} compare equal to \cs{snap@format}
+%    ensures that only one comparison is needed to tell if
+%    we shouldn't attempt to input the current file type.
+%    \begin{macrocode}
+  \let\snapx@application=\snapx@format \let\snapx@tfm=\snap@format
+  \@ifnextchar *\snap@store@version\snap@store@error#2*{end}{}{}%
+  \endgroup
+}
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+\@ifundefined{snap@fake@b}{}{%
+  \let\snap@store@b\snap@fake@input
+  \let\RequireVersions\rqvTest
+}
+%    \end{macrocode}
+%
+%    Compensate for a bug in old versions of \fn{amsgen.sty}. This is a
+%    little tricky.
+%
+%    Old version: \cs{ver@amsgen}=1996/10/29 v1.2b
+%
+%    New version: \cs{ver@amsgen.sty}=1999/11/30 v2.0
+%    \begin{macrocode}
+%\@namedef{ver@amsgen.sty}{1996/10/29 v1.2b}
+\AtBeginDocument{%
+  \@ifundefined{ver@amsgen}{}{%
+    \@xp\let\csname ver@amsgen.sty\@xp\endcsname
+                    \csname ver@amsgen\endcsname
+  }%
+}
+%    \end{macrocode}
+%
+%    Terminate here without touching \LaTeX{} internals, unless
+%    one of the relevant snapshot options was chosen.
+%    \begin{macrocode}
+\let\snap@compare@versions\@gobble \let\snap@check\@gobble
+\let\snap@selfcheck\@gobble \let\snap@selfcheck@a\@gobble
+\ifx\snap@select\@empty \endinput \fi
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+\begingroup \catcode`\.=11\relax
+\gdef\snap@selfcheck@b#1\rqv@snapshot.sty#2#3\@nil{T#2}
+\gdef\snap@selfcheck@a#1{%
+  \if\@xp\snap@selfcheck@b\csname rqv@#1\endcsname T%
+         \rqv@snapshot.sty F\@nil
+    \snap@check{#1}%
+  \fi
+}
+\endgroup
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+\def\@nofmt#1.fmt.#2 {#1 }
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+\def\snap@mismatch@a#1#2#3{%
+  \snap@mismatch{snapshot}{^^J%
+    \space\space Required version #2 of \@nofmt#1.fmt. and^^J%
+    \space\space provided version #3 do not match%
+  }\@ehc
+}
+%    \end{macrocode}
+%
+%    When comparing \cs{rqv@foo.sty} (information from a previous
+%    \latex/ run) with \cs{ver@foo.sty} (information from current run),
+%    we first call \cs{snap@trim@version} on the latter to clear away
+%    any idiosyncrasies in the contents.
+%    \begin{macrocode}
+\def\snap@compare@versions#1{%
+  \begingroup
+    \@ifundefined{rqv@#1}{}{%
+      \edef\0{\csname rqv@#1\endcsname}%
+      \edef\1{\csname ver@#1\endcsname}%
+      \edef\1{\@xp\snap@trim@version\1 v0.0 v0.0 \@nil}%
+      \edef\@tempa{\@xp\snap@select\0 v0.0 v0.0 \@nil}%
+      \edef\@tempb{\@xp\snap@select\1 v0.0 v0.0 \@nil}%
+      \ifx\@tempa\@tempb
+      \else
+        \edef\@tempd{\@nx\snap@mismatch@a{#1}{\@tempa}{\@tempb}}%
+        \@xp\@tempd
+      \fi
+    }%
+  \endgroup
+}
+%    \end{macrocode}
+%
+%    Because \cs{ProvidesFile} is used in \fn{.fd} files which are
+%    normally read with special catcodes, there tend to
+%    be problems with whitespace characters being erroneously lost from
+%    the second argument. Since we have to put in a \cs{snap@check} call
+%    anyway, while we're at it let's fix a bug of this type that
+%    affected some older versions of \latex/.
+%    \begin{macrocode}
+\def\ProvidesFile#1{%
+  \def\snap@checker{\snap@check{#1}}%
+  \begingroup
+    \aftergroup\snap@checker
+    \catcode`\ 10\catcode\endlinechar 10 %
+    \@makeother\/%
+    \@makeother\&%
+    \@ifnextchar[{\@providesfile{#1}}{\@providesfile{#1}[]}%
+}
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+\def\@pr@videpackage[#1]{%
+  \expandafter\xdef\csname ver@\@currname.\@currext\endcsname{#1}%
+  \ifx\@currext\@clsextension
+    \typeout{Document Class: \@gtempa\space#1}%
+  \else
+    \wlog{Package: \@gtempa\space#1}%
+  \fi
+  \snap@check{\@currname.\@currext}%
+}
+%    \end{macrocode}
+%
+%    The usual \cs{endinput} to ensure that random garbage at the end of
+%    the file doesn't get copied by \fn{docstrip}.
+%    \begin{macrocode}
+\endinput
+%    \end{macrocode}
+%
+% \section*{To Do}
+%
+% \begin{itemize}
+% \item Provide a test to distinguish between shared-use files and
+%    document-specific files? Document-specific files would be things
+%    like graphics files loaded via \cs{includegraphics} or book
+%    chapters loaded via \cs{include}. But there might also be something
+%    like \verb'\input{my-book-macros}' in the preamble. Maybe authors
+%    should be encouraged to put this after \verb'\begin{document}'? Or,
+%    even, after \verb'\begin{abstract}' so that the abstract will
+%    contain only lowest-common-denominator \LaTeX{} commands?
+%
+%    The non-document-specific files most commonly loaded after
+%    \verb'\begin{document}' would be \fn{.fd} files, but there is also
+%    the possibility of autoloaded stuff (\fn{alatex} format).
+% \end{itemize}
+%
+% \CheckSum{777}
+% \Finale
diff --git a/Master/texmf-dist/source/latex/snapshot/snapshot.ins b/Master/texmf-dist/source/latex/snapshot/snapshot.ins
new file mode 100644
index 00000000000..d30602c46ec
--- /dev/null
+++ b/Master/texmf-dist/source/latex/snapshot/snapshot.ins
@@ -0,0 +1,12 @@
+% Normal installation of this package in a standard TDS texmf tree:
+% Put snapshot.sty into the directory texmf/tex/latex/misc.
+% Put snapshot.dvi (produced by running LaTeX on snapshot.dtx) into
+% texmf/doc/latex/misc.
+
+\def\batchfile{snapshot.ins}
+\input docstrip.tex
+\preamble
+\endpreamble
+\keepsilent
+\generateFile{snapshot.sty}{f}{\from{snapshot.dtx}{}}
+\endinput