%\iffalse
%%======================NATBIB.DTX========================================
% This is a LaTeX package to modify \cite and \thebibliography for author-year 
%    systems of bibliographic citation; will also work with 
%    numerical systems, allowing simplified style changes for them too.
%     Docstrip options available:
%        package - to produce a .sty file with the uncommented coding
%        driver  - to produce a LaTeX2e driver file to print the documentation
%        209     - (with package) for package that runs under LaTeX 2.09 too
%        209     - (with driver) to produce LaTeX 2.09 driver
%        subpack - (with package) for coding included in other packages
%        all     - (with package) to include all author-year systems
%                   else individually with:
%        apalike, newapa, harvard, authordate, astron
%        agu     - (with package,subpack) for inclusion in aguplus package
%        nlinproc- (with package,subpack) for inclusion in nlinproc package
%     The unstripped version is equivalent to options <package,209>
%--------------------------------------------------------------------------
% In the documentation, the LaTeX2e font commands are emulated for 2.09 
% But otherwise, it must conform to LaTeX 2.09
%--------------------------------------------------------------------------
%<*package>
%\fi
\def\filename{natbib}
\def\fileversion{5.0}
\def\filedate{1994/05/18}
%\def\docdate{1994/05/18}
%\iffalse
%<*!subpack>
 %-------------------------------------------------------------------
 % NOTICE:
 % This file may be used for non-profit purposes.
 % It may not be distributed in exchange for money, 
 %   other than distribution costs.
 %   
 % The author provides it `as is' and does not guarantee it in any way.
 % 
%% Copyright (C) 1994 Patrick W. Daly
 % Max-Planck-Institut f\"ur Aeronomie
 % Postfach 20
 % D-37189 Katlenburg-Lindau
 % Germany
 % 
 % E-mail:
 % SPAN--     nsp::linmpi::daly    (note nsp also known as ecd1)
 % Internet-- daly@linax1.dnet.gwdg.de   
 %-----------------------------------------------------------
%   Version 4.0: 1993 Aug 19 - First issue with documentation
%   Version 4.1: 1993 Oct  4 - Simplification of \@citeapalk
%   Version 4.1a:1993 Oct 14 - Add rev option for reversed comments in \cite
%   Version 4.1b:1993 Oct 18 - Add \bibfont to list definition =\relax
%   Version 4.2 :1993 Oct 22 - Add coding for JGR, GRL, NLINPROC
%                     Nov 20 - Add coding for new AGU supplement
%   Version 4.3a:1994 Feb 24 - Begin LaTeX2e fixups
%   Version 5.0 :1994 May 18 - Convert to LaTeX2e; add \citeauthor, \citeyear;
%                              two optional texts for \cite, so rev option
%                              no longer needed; LaTeX2e options to choose
%                              punctuation.
%
%</!subpack>
%</package>
%\fi
% \CheckSum{642}
% \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         \~}
%
% \DoNotIndex{\@ifundefined,\@twoOninetrue,\addtolength,\begin}
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% \DoNotIndex{\ProvidesPackage,\RecordChanges,\space,\typeout,\usepackage}
% \DoNotIndex{\@auxout,\@for,\@gobble,\@ifnextchar,\@m,\@mkboth,\@nil}
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% \DoNotIndex{\citation,\clubpenalty,\CodelineNumbered,\csname}
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% \DoNotIndex{\relax,\section,\settowidth,\sfcode,\sloppy,\small,\string}
% \DoNotIndex{\theenumiv,\thepage,\unskip,\uppercase,\usecounter,\vskip}
% \DoNotIndex{\widowpenalty,\write,\xdef,\z@}
%
% \setcounter{IndexColumns}{2}
% \setlength{\IndexMin}{10cm}
% \setcounter{StandardModuleDepth}{1}
%
% ^^A Define the \cmd command for printing command names in \changes
% \def\cmd#1{\protect\texttt{\protect\bslash #1}}
% 
% \iffalse
%  Compatibilities for printing the documentation with LaTeX 2.09
%  or with LaTeX2e in 2.09 compatibility mode.
%  Define \p@LaTeX so it will change font (pure 2.09 only)
%  For pure 2.09 and 2.09 compatibility,
%    define \LaTeXe plus the 2e font commands and declarations.
% \fi
% \expandafter\ifx\csname if@compatibility\endcsname\iffalse\else
% \def\LaTeXe{\protect\pLaTeXe}
% \def\pLaTeXe{\mbox{%
%   \LaTeX\kern.15em$2_{\textstyle\varepsilon}$}}
% \fi
% \expandafter\ifx\csname if@compatibility\endcsname\relax
% \makeatletter
% \def\p@LaTeX{\@tempcnta=\the\fam \leavevmode L\raise.42ex
%    \hbox{$\fam\@tempcnta\scriptstyle\kern-.3em A$}\kern-.15em%
%     T\kern-.1667em\lower.7ex\hbox{E}\kern-.125emX}   
% \makeatother
%   \let\bfseries=\bf   \let\mdseries=\rm
%   \let\upshape=\rm    \let\itshape=\it
%   \let\slshape=\sl    \let\scshape=\sc
%   \let\sffamily=\sf   \let\rmfamily=\rm
%   \let\ttfamily=\tt   \let\normalfont=\rm
% \fi
% \expandafter\ifx\csname emph\endcsname\relax
%   \newcommand{\emph}[1]{{\em #1\/}}
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%   \newcommand{\textrm}[1]{{\rm #1}}
%   \newcommand{\textsc}[1]{{\sc #1}}
%   \newcommand{\textsl}[1]{{\sl #1\/}}
% \fi
%
% \changes{4.0}{1993 Aug 19}{First documented release}
% \changes{4.2}{1993 Oct 22}{Remove general coding for JGR, GRL, NLINPROC}
% \changes{4.2}{1993 Nov 20}{Remove more coding for AGU}
% \changes{4.3a}{1994 Feb 24}{First additions for \LaTeXe}
% \changes{5.0}{1994 May 18}{Revised for \LaTeXe{} and 2.09; remove
%          obsolete JGR, GRL coding.}
%
% \hyphenation{par-en-the-ti-cal}
%
% \title{{\bfseries Natural Sciences Citations and References}\\
%         (Author-Year and Numerical Schemes)}
%    
% \author{Patrick W. Daly\thanks
%               {This paper describes package
%               \texttt{\filename}, version \fileversion{} 
%               from \filedate.}}
%         
% \date{Documentation from \docdate\\[1ex]
% \textsl{This is part of the \texttt{preprint} collection of style packages}
% \\[1ex]
% \fbox{\bfseries This package may be used for both \LaTeXe{} and \LaTeX~2.09}}
% 
% \maketitle
%
% \MakeShortVerb{\|}
% 
% \pagestyle{myheadings}
% \markright{NATURAL SCIENCES CITATIONS AND REFERENCES}
%
% \newcommand{\btx}{\textsc{Bib}\TeX}
% \newcommand{\thestyle}{\texttt{\filename}}
%
% \begin{abstract}
% Journals in the natural sciences tend to use the author-year style of
% literature citations, in contrast to the numerical style supported by
% \LaTeX{} and \btx. A number of style options exist to accommodate this
% scheme, but with various new sets of |\cite| commands and a variety of
% ways of entering the information in the |\bibitem| entry. Instead, 
% \thestyle\texttt{.sty}
% uses the |\cite| command almost exactly as provided in
% original \LaTeX, and yet can read in the |\bibitem| information in all
% the formats available.
% 
% Even those journals that do use numbered citations exhibit a
% variety of styles that are not so easy to reprogram into \LaTeX.
% This style option offers an interface for both author-year and numerical
% styles, with a means to redefine the citation format automatically based
% on the name of the style in the |\bibliographystyle| command. For
% example, by selecting the style \texttt{nature}, then the style of references 
% is that of the journal \textsl{Nature}, i.e., as superscript numbers. It is
% easy to add new definitions to \thestyle\texttt{.sty} for other bibliographic
% styles.
% 
% Thus \thestyle\texttt{.sty} can act as a single style option for all
% bibliographic styles available.
% \end{abstract}  
% 
%\iffalse
% The stripped version of this file contains the following brief description:
%<*package&!subpack>
 % Intended mainly for author-year style citations, but will work with
 % numericals as well.
 % 
 % If author-year style selected, then \bibitem must have one of the
 %   following forms:
 %   \bibitem[Jones et al.(1990)]{key}...
%<*apalike|authordate|all>
 %   \bibitem[Jones et al., 1990]{key}...
%</apalike|authordate|all>
%<*newapa|all>
 %   \bibitem[\protect\citeauthoryear{Jones, Baker, and Williams}{Jones
 %       et al.}{1990}]{key}...
 %   \bibitem[\protect\citeauthoryear{Jones et al.}{1990}]{key}...
%</newapa|all>
%<*astron|all>
 %   \bibitem[\protect\astroncite{Jones et al.}{1990}]{key}...
%</astron|all>
%<*authordate|all>
 %   \bibitem[\protect\citename{Jones et al., }1990]{key}...
%</authordate|all>
%<*harvard|all>
 %   \harvarditem[Jones et al.]{Jones, Baker, and Williams}{1990}{key}...
%</harvard|all>
 %   
 % This is either to be made up manually, or to be generated by an 
 % appropriate .bst file with BibTeX.
 % 
 % Then, \cite{key}  ==>>  Jones et al. (1990)
 %       \cite[]{key} ==>> (Jones et al., 1990)
 % Multiple citations as normal:
 %       \cite[]{key1,key2} ==>> (Jones et al., 1990; Smith, 1989)
 %                           or  (Jones et al., 1990, 1991)
 % Optional notes as:
 %   \cite[chap. 2]{key}    ==>> (Jones et al., 1990, chap. 2)
 %   \cite[e.g.,][]{key}    ==>> (e.g., Jones et al., 1990)
 %   \cite[see][pg. 34]{key}==>> (see Jones et al., 1990, pg. 34)
 %  (Note: in standard LaTeX, only one note is allowed, after the ref.
 %   Here, one note is like the standard, two make pre- and post-notes.)
 %
 % Additional citation possibilities (author-year only)
 %   \citeauthor{key}  ==>> Jones et al.
 %   \citeyear{key}    ==>> 1990
 % (Multiple keys NOT allowed!)
 %
 % Defining the citation style of a given bib style:
 % Use \bibpunct with 6 arguments:
 %    1. opening bracket for citation
 %    2. closing bracket
 %    3. citation separator (for multiple citations in one \cite)
 %    4. the letter n for numerical styles, else anything for author-year
 %    5. punctuation between authors and date
 %    6. punctuation between years when common authors missing
 % Example (and default) \bibpunct{(}{)}{;}{a}{,}{,}
 % 
 % To make this automatic for a given bib style, named newbib, say, add
 % to this style file
 %   \bibstyle@newbib{\bibpunct... + any other redefinitions (see examples)}
 % Then the \bibliographystyle{newbib} will cause \bibstyle@newbib to 
 % be called on THE NEXT LATEX RUN (via the aux file).
 %
 % LaTeX2e Options: (for selecting punctuation)
 %   round  -  round parentheses are used (default)
 %   square -  square braces are used
 %   colon  -  multiple citations separated by colon (default)
 %   comma  -  separated by comma
 %   authoryear - selects author-year citations (default)
 %   numbers-  selects numerical citations
 %   nobibstyle - deactivates punctuation selection via \bibliographystyle
 % Note: normally the punctuation style defined by \bibstyle@xxx and invoked
 %       with \bibliographystyle{xxx} dominates; with option nobibstyle
 %       this is no longer the case.
 % LaTeX2e options are called as, e.g.
 %        \usepackage[square,comma]{natbib}
 %-----------------------------------------------------------
%</package&!subpack>
%\fi
%
% \section{Introduction}
% The first problem of using author-year literature citations with standard
% \LaTeX{} is that the two forms of citations are not supported. These are:
% \begin{quote}
% textual: \dots\ as shown by Jones et al. (1990) \dots\\
% parenthetical: It has been shown (Jones et al., 1990) that \dots
% \end{quote}
% There is only one |\cite| command to do both jobs.
% 
% A second problem is that the \texttt{thebibliography} environment for
% listing the references insists on including the {\em labels\/} in the
% list. These labels are normally the numbers, needed for referencing. In
% the author-year system, they are superfluous and should be left off.
% Thus, if one were to make up a bibliography with the author-year as
% label, as
% \begin{quote}
% \begin{verbatim}
% \begin{thebibliography}{...}
% \bibitem[Jones et al., 1990]{jon90}
% Jones, P. K., . . .
% \end{thebibliography}
% \end{verbatim}
% \end{quote}
% then |\cite{jon90}| produces the parenthetical citation [Jones et al.,
% 1990], but there is no way to get the textual citation. Furthermore,
% the citation text will also be included in the list of references. 
% 
% The final problem is to find a \btx{} bibliography style that will be
% suitable.
% 
% \section{Previous Solutions}
% Although the author-year citation style is not supported by {\em
% standard\/} \LaTeX, there are a number of private styles around that have
% worked on this problem. The various bibliographic styles (\texttt{.bst}
% files) that exist are usually tailored to be used with a particular
% \LaTeX{} style option.
% 
% I have found a large number of \texttt{.bst} files on file servers that may
% act as indicators of the various systems available.
% 
% \subsection{The \texttt{natsci.bst} Style}
% What gave me my first inspiration was Stephen Gildea's \texttt{natsci.bst}
% for use with his \texttt{agujgr.sty} file. This showed me that the problem
% was solvable. However, Gildea's style formats |\bibitem| just as I
% illustrated above: with an optional label consisting of abbreviated
% authors and year. Thus only parenthetical citations can be accommodated.
% The list of references, however, is fixed up in his style files.
% 
% One serious drawback of \texttt{natsci.bst} is that it has been written for
% \btx{} version~0.98, which is no longer current. It could be converted to
% version~0.99 by replacing every occurrence of |:=| by |swap$ :=|.
% 
% \subsection{The \texttt{apalike.bst} Style}
% Oren Patashnik, the originator of \btx{} and the standard \texttt{.bst}
% files, has also worked on an author-year style, called \texttt{apalike.bst}
% with a corresponding \texttt{apalike.sty} to support it. Again, only the
% parenthetical citation is provided. Except for the fact that his style
% works with version~0.99 of \btx, its functionality is identical to that
% of the \texttt{natsci} files.
% 
% Patashnik does not like author-year citations. He makes this very clear
% in his \btx{} manuals and in the header to \texttt{apalike.bst}.
% Nevertheless, one should respect his work in this area, simply because he
% should be the best expert on matters of \btx. Thus \texttt{apalike.bst}
% could be the basis for other styles.
% 
% The form of the \texttt{thebibliography} entries in this system is
% \begin{quote}
% |\bibitem[Jones et al., 1990]{jon90}...|
% \end{quote}
% the same as I illustrated above. This is the most minimal form that can
% be given. I name it the \texttt{apalike} variant, after Patashnik's 
% \texttt{apalike.bst} and \texttt{apalike.sty}. However, there could be many
% independent \texttt{.bst} files that follow this line.
% 
% The bibliography style files belonging to this group include:
% \begin{quote}
% \texttt{apalike}, \texttt{apalike2}, \texttt{cea}, \texttt{cell}, 
% \texttt{jmb}, \texttt{phapalik}, \texttt{phppcf}, \texttt{phrmp}
% \end{quote}
% 
% \subsection{The \texttt{newapa} Style}
% A major improvement has been achieved with \texttt{newapa.bst} and the
% accompanying \texttt{newapa.sty} files by Stephen N. Spencer and Young U.
% Ryu. Under their system, three separate items of information are included
% in the |\bibitem| label, to be used as required. These are: the full
% author list, the abbreviated list, and the year. This is accomplished by
% means of a |\citeauthoryear| command included in the label, as
% \begin{quote}
% |\bibitem[\protect\citeauthoryear{Jones, Barker,|\\
% |  and Williams}{Jones et al.}{1990}]{jon90}...|
% \end{quote}
% Actually, this only illustrates the basic structure of |\citeauthoryear|;
% the \texttt{newapa} files go even further to replace some words and 
% punctuation
% with commands. For example, the word `and' above is really
% |\betweenauthors|, something that must be defined in the \texttt{.sty} file.
% Of course, |\citeauthoryear| is also defined in that file. A
% number of different |\cite| commands are available to print out the
% citation with complete author list, with the short list, with or without
% the date, the textual or parenthetical form. 
% 
% Thus the |\citeauthoryear| entry in |\bibitem| is very flexible,
% permitting the style file to generate every citation form that one might
% want. It is used by a number of other styles, with corresponding
% \texttt{.sty} files. They all appear to have been inspired by 
% \texttt{newapa.bst}, although they lack the extra punctuation commands. 
% 
% Bibliographic style files belonging to the \texttt{newapa} group include
% \begin{quote}
% \texttt{newapa}, \texttt{chicago}, \texttt{chicagoa}, \texttt{jas99}, 
% \texttt{named}
% \end{quote}
% Note: the last of these, \texttt{named.bst}, uses |\citeauthoryear| in a
% slightly different manner, with only two arguments: the short list and
% year.
% 
% \subsection{The Harvard Family}
% The same effect is achieved by a different approach in the Harvard family
% of bibliographic styles. Here a new substitute for |\bibitem| is used, as
% \begin{quote}
% |\harvarditem[Jones et al.]{Jones, Baker, and|\\
% |   Williams}{1990}{jon90}...|
% \end{quote}
% The accompanying interfacing style file is called \texttt{harvard.sty}. It
% defines |\harvarditem| as well as the citation commands |\cite|, for
% parenthentical, and |\citeasnoun|, for textual citations. The first
% citation uses the long author list, following ones the shorter list, if
% it has been given in the optional argument to |\harvarditem|.
% 
% Bibliography styles belonging to the Harvard family are
% \begin{quote}
% \texttt{agms}, \texttt{dcu}, \texttt{kluwer}
% \end{quote}
% 
% My personal feeling is that the Harvard method unnecessarily adds a new
% command. The same thing is achieved more consistently with standard
% \LaTeX{} with the |\citeauthoryear| command.
% 
% \subsection{The Astronomy Style}
% Apparently realizing the limitations of his \texttt{apalike} system, Oren
% Patashnik went on to develop a `true' \texttt{apa} bibliographic style,
% making use of the method already employed by an astronomy journal. This
% is actually very similar to the \texttt{newapa} label but with only the
% short list of authors:
% \begin{quote}
% |\bibitem[\protect\astroncite{Jones et al.}{1990}]{jon90}|\\
% |   ...|
% \end{quote}
% It requires the style file \texttt{astron.sty} (which I have not yet been
% able to obtain), or any other style that defines |\astroncite|
% appropriately.
% 
% Bibliographic styles belonging to the astronomy group are
% \begin{quote}
% \texttt{apa}, \texttt{astron}, \texttt{bbs}, \texttt{cbe}, 
% \texttt{humanbio}, \texttt{humannat}, \texttt{jtb}
% \end{quote}
% 
% This is as good as the |\citeauthoryear| command, although not as
% flexible since the full list of authors is missing.
% 
% \subsection{The \texttt{authordate} Style}
% Finally, I have also found some styles making use of a label command
% called |\citename| in the form
% \begin{quote}
% |\bibitem[\protect\citename{Jones et al., }1990]{jon90}|\\
% |    ...|
% \end{quote}
% 
% This is not a good system since the author list and date are not cleanly
% separated as individual arguments, and since the punctuation is included
% in the label text. It is better to keep the punctuation fully removed, as
% part of the definitions in the \texttt{.sty} file, for complete flexibility.
% 
% Bibliographic styles belonging to this group are
% \begin{quote}
% \texttt{authordate1}, \texttt{authordate2}, \texttt{authordate3}, 
% \texttt{authordate4}, \texttt{aaai-named}
% \end{quote}
% with accompanying style file \texttt{authordate1-4.sty}.
% 
% \section{The \thestyle{} System}
% The form of the |\bibitem| entry that I have used for all by
% bibliographic styles is only slightly more complicated than the minimal
% one, but allows a clean separation between authors and date:
% \begin{quote}
% |\bibitem[Jones et al.(1990)]{jon90}...|
% \end{quote}
% The separation can be done be using the parentheses as delimiters to an
% appropriate command. Parentheses are used no matter what characters are
% actually to surround the citation.  The minimal (\texttt{apalike}) system
% can also have the authors and year separated, but only by assuming that
% the authors are divided from the year by comma and blank. If the author
% list itself contains a comma and blank, the separation will be incorrect.
% 
% My system, called \thestyle{} for `natural sciences bibliography',
% admittedly does not contain the full author list in the citation label,
% something that I have never needed. However, its advantage over the 
% \texttt{newapa} style is that for someone typing his \texttt{thebibliography}
% environment by hand, without \btx, there is less work to be done. This is
% of no importance if one uses \btx{} as one should!
% 
% My package,\footnote{Formerly called a \emph{style file} in the older
% \LaTeX~2.09 terminology.}
% \thestyle\texttt{.sty}, supports my own |\bibitem| format, as
% The additional questions of punctuation (type of brackets, commas or
% semi-colons between citations) can be defined once and for all for each
% \texttt{.bst} file and need never be specified explicitly in the source text.
% The use of |\cite| is the same for all citation styles, meaning that the
% additional features that might be available in the `proper' \texttt{.sty}
% file will be missing. (This could be changed later.) The result is a
% single \LaTeX{} style file to handle {\em all\/} the bibliographic
% citation styles in a uniform manner.
% 
% As of version 5.0 (1994 May 18), the package accommodates the new
% standard \LaTeXe, although compatibility with the older \LaTeX~2.09 is
% maintained, at least with a \texttt{docstrip} option. A pure \LaTeXe{}
% version of the \texttt{.sty} file can be made be leaving off this
% \texttt{209} option.
% 
% \subsection{Usage of this Package}
% \DescribeMacro{\cite}
% The \thestyle{} package makes use of the |\cite| command in precisely
% the same manner as in standard \LaTeX, unlike all the other author-year
% interface style options. The distinction between parenthetical and
% textual citations is made by means of the optional argument to |\cite|,
% which only has meaning in the parenthetical case. Thus a null optional
% argument indicates a citation in parentheses.
% \begin{quote}
% \begin{tabular}{l@{\quad$\Rightarrow$\quad}l}
%   |\cite{jon90}| & Jones et al. (1990)\\
%   |\cite[]{jon90}| & (Jones et al., 1990)\\
%   |\cite[chap.~2]{jon90}| & (Jones et al., 1990, chap.~2)
% \end{tabular}
% \end{quote}
% 
% A new feature not in standard \LaTeX{} is the possibility of adding a
% second optional text, for notes before and after the citation. (In
% earlier versions, I provided a single note either before or after,
% selectable with a \texttt{docstrip} option; this option is no longer
% needed.)
% \begin{quote}
% \begin{tabular}{l@{\quad$\Rightarrow$\quad}l}
%   |\cite[e.g.,][]{jon90}| & (e.g., Jones et al., 1990)\\
%   |\cite[see][pg.~34]{jon90}| & (see Jones et al., 1990, pg.~34)
% \end{tabular}
% \end{quote}
% Beware: a single optional note goes \emph{after} the citation, as in
% normal \LaTeX; with two notes, the first goes \emph{before}, the second
% \emph{after}.
% 
% Multiple citations may be made as usual, by including more than one
% citation key in the |\cite| command argument. \textsl{If adjacent citations
% have the same author designation but different years, then the author
% names are not reprinted.}
% \begin{quote}
% \begin{tabular}{l@{\quad$\Rightarrow$\quad}l}
%   |\cite{jon90,jam91}| & Jones et al. (1990); James et al. (1991)\\
%   |\cite[]{jon90,jam91}| & (Jones et al., 1990; James et al. 1991)\\
%   |\cite[]{jon90,jon91}| & (Jones et al., 1990, 1991)
% \end{tabular}
% \end{quote}
% 
% \DescribeMacro{\citeauthor}
% \DescribeMacro{\citeyear}
% In author-year schemes, it is sometimes desirable to be able to refer to
% the authors without the year, or vice versa. This is provided with two
% extra commands
% \begin{quote}
% \begin{tabular}{l@{\quad$\Rightarrow$\quad}l}
%   |\citeauthor{jon90}| & Jones et al.\\
%   |\citeyear{jon90}|   & 1990
% \end{tabular}
% \end{quote}
% Multiple citations are \emph{not} allowed with these commands. If they
% are used with a numerical citation scheme, they produce warning messages.
% 
% \DescribeMacro{\bibpunct}
% The above examples have been printed with the default set of punctuation.
% It is possible to change this, as well as to select numerical or
% author-year style, by means of the |\bibpunct| command, which takes 6
% arguments:
% \begin{enumerate}
% \item the opening bracket symbol, default = `(';
% \item the closing bracket symbol, default = `)';
% \item the punctuation between multiple citations, default = `;';
% \item the letter `n' for numerical style, any other letter for
%       author-year, default = author-year; note, it is not necessary to
%       specify which author-year interface is being used, for all will be
%       recognized;
% \item the punctuation that comes between the author names and the year
%       (parenthetical case only), default = `,';
% \item the punctuation that comes between years when common author lists
%       are suppressed, default = `,'.
% \end{enumerate}
% 
% The |\bibpunct| command must be issued before the first |\cite| command,
% and after |\begin{document}|.
% 
% Example, |\bibpunct{[}{]}{,}{a}{}{;}| would change the output from
% |\cite[]{jon90,jon91,jam92}| to [Jones et al. 1990; 1991, James et al.
% 1992].
% 
% \DescribeMacro{\bibstyle@xxx}
% Usually the punctuation style is determined by the journal for which one
% is writing, and is as much a part of the bibliography style as everything
% else. It would therefore make more sense if it could be included in the
% \texttt{.bst} file. This is conceivable, and may be considered as a future
% extension.
% 
% For now, however, in order to avoid having to specify the punctuation
% style explicitly in every document (and possibly having to change it if
% the article is submitted to another journal), \thestyle{} allows
% punctuation definitions to be directly coupled to the
% |\bibliographystyle| command that must always be present when \btx{} is
% used. It is this command that selects the \texttt{.bst} file; by adding such
% a coupling to \thestyle{} for every \texttt{.bst} file that one might
% want to use, it is not necessary to add |\bibpunct| explicitly in the
% document itself, unless of course one wishes to override the preset
% values.
% 
% Such a coupling is achieved by defining a command |\bibstyle@|{\em bst},
% where {\em bst\/} stands for the name of the \texttt{.bst} file. For example,
% the American Geophysical Union (AGU) demands in its publications that
% citations be made with square brackets and separated by semi-colons. I
% have an \texttt{agu.bst} file to accomplish most of the formatting, but such
% punctuations are not included in it. Instead, \thestyle{} has the
% definition
% \begin{quote}
% |\def\bibstyle@agu{\bibpunct{[}{]}{;}{a}{,}{,}}|
% \end{quote}
% 
% These style defining commands may contain more than just |\bibpunct|.
% Some numerical citation scheme require even more changes. For example,
% the journal \textsl{Nature} uses superscripted numbers for citations. To
% accommodate this, \thestyle{} contains the style definition
% \begin{quote}\begin{verbatim}
% \def\bibstyle@nature{\bibpunct{}{}{,}{n}{}{}%
%      \gdef\@biblabel##1{##1.}%
%      \gdef\@cite##1##2##3{\unskip\mbox{$^{##1}$}}}
% \end{verbatim}
% \end{quote}
% The redefined |\@biblabel| command specifies how the reference numbers
% are to be formatted in the list of references itself, while |\@cite|
% defines the appearance of the citations themselves. The redefinitions
% must be made with |\gdef|, not |\def|.
% 
% The selected punctuation style and other redefinitions will not be in
% effect on the first \LaTeX{} run, for they are stored to the auxiliary
% file for the subsequent run.
% 
% \DescribeMacro{\bibfont}
% The list of references is normally printed in the same font size and
% style as the main body. However, it is possible to define |\bibfont|
% to be font commands that are in effect within the \texttt{thebibliography}
% environment.
%
% \subsection{Options with \LaTeXe}
% The new (mid-1994) \LaTeX{} standard replaces \emph{style options} by
% \emph{packages}, although both bear the extension \texttt{.sty}. Most
% style options written for the older \LaTeX~2.09 will run as packages
% under \LaTeXe. Version 5.0 of \thestyle{} is intended to run under the
% newer standard, but will also run under the older one, at least if the
% \texttt{docstrip} option \texttt{209} has been used during the
% extraction.
% 
% One of the new features of \LaTeXe{} is \emph{options} for the packages,
% in the same way as main styles (now called \emph{classes}) can take
% options. This package is now installed with
% \begin{quote}
% |\documentclass[..]{...}|\\
% |\usepackage[|\emph{options}|]{|\thestyle|}|
% \end{quote}
% The options available provide another means of specifying the
% punctuation for citations:
% \begin{description}
% \item[\ttfamily round] (default) for round parentheses;
% \item[\ttfamily square] for square brackets;
% \item[\ttfamily colon] (default) to separate multiple citations with
%      colons;
% \item[\ttfamily comma] to use commas as separaters;
% \item[\ttfamily authoryear] (default) for author-year citations;
% \item[\ttfamily numbers] for numerical citations;
% \item[\ttfamily super] for superscripted numerical citations, as in
%      \textsl{Nature};
% \item[\ttfamily nobibstyle] to ignore punctuation style specified by
%      |\bibliographystyle|.
% \end{description}
% 
% The last option, \texttt{nobibstyle}, is necessary if the punctuation
% specified by the options is to dominate over any pre-programmed ones
% given by a |\bibstyle@xxx|. For example, to use the \texttt{plain.bst}
% format for the bibliography with superscripted citations, one gives
% \begin{quote}
% |\documentclass{article}|\\
% |\usepackage[super,nobibstyle]{|\thestyle|}|\\
% |. . . . .|\\
% |\bibliographystyle{plain}|
% \end{quote}
% 
% {\slshape Any punctuation style set with |\bibpunct| always has topmost 
% priority!}
% 
% \subsection{As Module to Journal-Specific Styles}
% Although \thestyle{} is meant to be an all-purpose bibliographic style
% \emph{package}, it may also be incorporated as a module to other 
% packages for specific journals. In this case, many of the general features may
% be left off. This is allowed for with \texttt{docstrip} options that not
% only leave off certain codelines, but also include extra ones. So far,
% options exist for 
% \begin{description}
% \item[\ttfamily nlinproc] for \textsl{Nonlinear Processes in Geophysics},
% \item[\ttfamily agu] for \textsl{American Geophysical Union} journals.
% \end{description}
% 
% Previous options \texttt{jgr} and \texttt{grl} have become obsolete due
% to revisions in these journals; they have been replaced by the more
% general \texttt{agu} option.
%
% \StopEventually{
% \section{Summary}
% The \thestyle{} package offers a powerful interface for almost all
% existing \btx{} style files. It handles both numerical and author-year
% citations with a uniform usage of the {\ttfamily\bslash cite} command. 
% Additional modifications that depend on the \texttt{.bst} file selected,
% and which are normally included in separate style option files designed
% just for that bibliographic style, may easily be added to \thestyle{} for
% automatic implementation in the source text. Thus \thestyle{} represents
% a universal interface for all citation schemes.
% }
% 
% \section{The Coding}
% This section presents and explains the actual coding of the macros.
% It is nested between |%<*package>| and |%</package>|, which
% are indicators to \texttt{docstrip} that this coding belongs to the package 
% file.
%
% The \texttt{docstrip} option \texttt{subpack} should only be called if the
% coding is to be included as part of another package, in which case the 
% announcement text and \LaTeXe{} options are suppressed.
%
% A number of other \texttt{docstrip} options are available in order to 
% include coding for the other types of author-year interfaces:
% \begin{description}
% \item[\ttfamily all] includes all of the other interfaces;
% \item[\ttfamily apalike] allows interpretation of minimal \texttt{apalike} 
%    form of |\bibitem|;
% \item[\ttfamily newapa] allows |\citeauthoryear| to be in the optional argument to
%    |\bibitem| along with the punctuation commands of \texttt{newapa.sty};
% \item[\ttfamily harvard] includes interpretation of |\harvarditem|;
% \item[\ttfamily astron] allows |\astroncite| to appear in the optional argument
%    of |\bibitem|;
% \item[\ttfamily authordate] adds the syntax of the |\citename| command.
% \end{description}
%
% This style option file is intended to act as a module for main styles
% files written for specific journals, in which case the flexible
% |\bibstyle@|{\em bst\/} commands are not wanted. Punctuation and
% other style features are to be rigidly fixed. These journal options are
% \begin{description}
% \item[\ttfamily agu] for journals of the \textsl{American Geophysical
%   Union};
% \item[\ttfamily nlinproc] for \textsl{Nonlinear Processes in Geophysics}.
% \end{description}
%
% The remaining options are:
% \begin{description}
% \item[\ttfamily package] to produce a \texttt{.sty} package file with most
%     comments removed;
% \item[\ttfamily 209] for a package file that will also run under the older
%     \LaTeX~2.09 and not just under the newer (mid-1994) \LaTeXe;
% \item[\ttfamily subpack] (together with \texttt{package}) for coding that 
%     is to be included inside a larger package; even more comments are 
%     removed, as well as \LaTeXe{} option handling and identification;
% \item[\ttfamily driver] to produce a driver \texttt{.drv} file that will print
%     out the documentation under \LaTeXe; with the \texttt{209} option, 
%     a driver \texttt{.209} file is also produced, for printing the
%     documentation under \LaTeX~2.09.
% \end{description}
% If the \thestyle\texttt{.dtx} file is renamed \thestyle\texttt{.sty},
% the result is equivalent to the options \texttt{package,209,all}.
% 
% The first thing is to type out the file name and version number to
% the monitor.
%    \begin{macrocode}
%<*package>
%<*!subpack>
\typeout{Package: `\filename' v\fileversion\space <\filedate> --P.W.Daly}
%</!subpack>
%    \end{macrocode}
%
% \begin{macro}{\if@twoOnine}
% This package is to work differently for \LaTeXe{} and \LaTeX~2.09, so it
% needs a flag that is \meta{true} for 2.09 or for \LaTeXe{} in compatibility 
% mode.
%    \begin{macrocode}
%<*209>
\newif\if@twoOnine \let\if@twoOnine=\if@compatibility
\@ifundefined{documentclass}{
    \@twoOninetrue
}{
%</209>
%<*!subpack>
    \NeedsTeXFormat{LaTeX2e}
    \ProvidesPackage{\filename}[\filedate\space (PWD)]
%</!subpack>
%<*209>
}
%</209>
%    \end{macrocode}
% \end{macro}    
%
% \subsection{Selection Citation Punctuation and Other Modifications}
% We begin by defining a number of punctuation styles for specific
% author-year \texttt{.bst} files that I use. 
% They are placed here, near the beginning, so that another
% user can easily find them to add his own. Some comments remain in the
% stripped version too.
% \begin{macro}{\bibstyle@xxx}
%    \begin{macrocode}
%<*!agu&!nlinproc>
 % Define citation punctuation for some author-year styles
 % One may add and delete at this point
\def\bibstyle@aa{\bibpunct{(}{)}{;}{a}{}{,}}
\def\bibstyle@pass{\bibpunct{(}{)}{;}{a}{,}{,}}
\def\bibstyle@anngeo{\bibpunct{(}{)}{;}{a}{,}{,}}
%</!agu&!nlinproc>
%<*!nlinproc>
\def\bibstyle@agu{\bibpunct{[}{]}{;}{a}{,}{,}}
%</!nlinproc>
%<*!agu>
\def\bibstyle@nlinproc{\bibpunct{(}{)}{;}{a}{,}{,}}
%</!agu>
%    \end{macrocode}
% Next, the same thing is done for some numerical styles. A major
% difference here is that the |\@biblabel| and |\@cite| commands must also
% be redefined in many cases. These redefinitions must be made with the
% |\gdef| (global definition) command.
%    \begin{macrocode}
%<*!agu&!nlinproc>
 % Define citation punctuation for some numerical styles
 % One may add and delete at this point
\def\bibstyle@cospar{\bibpunct{/}{/}{,}{n}{}{}%
     \gdef\@biblabel##1{##1.}}
\def\bibstyle@esa{\bibpunct{(}{)}{,}{n}{}{}%
     \gdef\@biblabel##1{##1.\hspace{1em}}%
     \gdef\@cite##1##2##3{\@citebegin Ref.~##1\if@tempswa,
          ##3\fi\@citeend}}
\def\bibstyle@nature{\bibpunct{}{}{,}{n}{}{}%
     \gdef\@biblabel##1{##1.}%
     \gdef\@cite##1##2##3{\unskip\mbox{$^{##1}$}}}
%    \end{macrocode}
% Note that the \textsl{Nature} |\@cite| ignores the optional notes (|##2|
% and |##3|) since it is not at all clear to me how I can add them to
% superscripts.
% 
% Finally, the standard \LaTeX{} (numerical) citation styles are included.
%    \begin{macrocode}
 % The standard LaTeX styles
\def\bibstyle@plain{\bibpunct{[}{]}{,}{n}{}{}}
\let\bibstyle@alpha=\bibstyle@plain
\let\bibstyle@abbrv=\bibstyle@plain
\let\bibstyle@unsrt=\bibstyle@plain
%</!agu&!nlinproc>
%    \end{macrocode}
% \end{macro}
% 
% \subsection{\LaTeXe{} Options}
% \begin{macro}{\DeclareOption}
% \changes{5.0}{1994 May 18}{Add \LaTeXe{} options.}
% For \LaTeXe, we can define some options to be used with the |\usepackage|
% command that loads the \thestyle{} package. These are an additional means
% of specifying the citation punctuation and scheme.
%    \begin{macrocode}
%<*!subpack>
%<*209>
\if@twoOnine\else
%</209>
\DeclareOption{round}{\def\@citebegin{(} \def\@citeend{)}}
\DeclareOption{square}{\def\@citebegin{[} \def\@citeend{]}}
\DeclareOption{comma}{\def\@citesep{,}}
\DeclareOption{colon}{\def\@citesep{;}}
\DeclareOption{numbers}{\let\@bibsetup=\@bibsetnum
   \let\@citex=\@citexnum
   \let\@biblabel=\@biblabelnum
   \let\@cite=\@citenum
   \ExecuteOptions{square,comma}}
\DeclareOption{super}{\ExecuteOptions{numbers}%
      \def\@cite##1##2##3{\unskip\mbox{$^{##1}$%
          \if@tempswa(##3)\fi}}}
\DeclareOption{authoryear}{}
\DeclareOption{nobibstyle}{\let\bibstyle=\@gobble}
%<*209>
\fi
%</209>
%</!subpack>
%    \end{macrocode}
% Note that any punctuation specified with these options will have the
% lowest priority: they can be overwritten by |\bibpunct| (highest
% priority) and by |\bibstyle| in the auxiliary file. The option
% \texttt{nobibstyle} turns off this last feature so that any pre-defined
% punctuation associated with the argument of |\bibliographystyle| will
% have no effect.
% \end{macro}
%
% \subsection{Internal Citing Macros}
% A number of internal macros (|\@citex|, |\@cite|, |\@biblabel|, and
% |\@bibsetup|) need to have different definitions for author-year and
% numerical schemes. For this reason, they are defined here, before the
% \LaTeXe{} options are executed. They are defined by default to be the
% author-year versions, and then |\let|ted to the numerical equivalent if
% necessary.
% 
% \begin{macro}{\@cite}
% \changes{4.2}{1993 Dec 2}{Reversed optional text no longer needs to include
%       a trailing blank}
% \changes{5.0}{1994 May 18}{Add optional notes after as well as before
%      citation.}
% \begin{macro}{\@citenum}
% \changes{5.0}{1994 May 18}{Add optional notes after as well as before
%      citation.}
% Define the internal |\@cite| command that prints the assembled string
% of citation label texts, plus possible optional notes, before and after.
% The numerical version is almost the same, except that the brackets
% |\@citebegin| and |\@citeend| are always present. The switch
% |\if@tempswa| is \meta{true} if optional arguments were present in the
% calling |\cite| command. For author-year, this distinguishes between
% parenthetical and textual citations.
%    \begin{macrocode}
\def\@cite#1#2#3{\if@tempswa\@citebegin\if#2\@empty\else#2 \fi
        #1\if#3\@empty\else, #3\fi\@citeend\else#1\fi}
%<*!agu&!nlinproc>
\def\@citenum#1#2#3{\@citebegin\if@tempswa\if#2\@empty\else#2 \fi\fi
   #1\if#3\@empty\else, #3\fi\@citeend}
%</!agu&!nlinproc>
%    \end{macrocode}
% \end{macro}\end{macro}
% 
% \begin{macro}{\@citexnum}
% The original definition of |\@citex| is now used to define |\@citexnum|,
% the version for numerical citations. What it does is to write a
% |\citation| command to the auxiliary file (for \btx), and then parses the
% second argument, the list of citation keys. These keys have to be decoded
% into the actual label text contained in |\b@|{\em key\/} (a number or
% author-year), and put together as the argument of |\@cite|. 
% 
% The temporary command |\@citeb| takes on the value of each of the keys in
% turn; |\@citea| is the separator between multiple citations, initially
% set to nothing, becoming |\@citesep| plus line-break suppression
% afterwards. The |\@tempa| construction removes any leading blanks in
% |\@citeb|, making |\cite{key1, key2}| possible. If |\b@|{\em key\/} is
% not defined (as on the first run, for example), a warning is printed, and
% a question mark inserted. Finally, the decoded label text is placed into
% an |\hbox| to prevent it from being split.
% \begin{macrocode} 
%<*!agu&!nlinproc>
\def\@citexnum[#1][#2]#3{\if@filesw\immediate\write
      \@auxout{\string\citation{#3}}\fi
  \let\@citea\@empty
  \@cite{\@for\@citeb:=#3\do
    {\@citea\def\@citea{\@citesep\penalty\@m\ }%
     \def\@tempa##1##2\@nil{\edef\@citeb{\if##1\space##2\else##1##2\fi}}%
     \expandafter\@tempa\@citeb\@nil
     \@ifundefined{b@\@citeb}{{\reset@font\bfseries ?}\@warning
       {Citation `\@citeb' on page \thepage \space undefined}}%
     \hbox{\csname b@\@citeb\endcsname}}}{#1}{#2}}
%</!agu&!nlinproc>
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@citex}
% The author-year version of |\@citex| is now defined as the default.
% It starts off much the same as the numerical version. However, it wants
% the authors and year for each decoded label text to be separated into
% |\@citenm| and |\@citedt|. This is done by the routine |\@cite@parse|.
% The names of the authors in the previous key are stored in |\@citemm|,
% and if that is the same as the current names, it is not printed again.
% The output citation text is not put into an |\hbox| since line division
% may occur within the author-year citation. The output is formatted
% differently for parenthetical (|\@tempswa| \meta{true}) and textual
% (|\@tempswa| \meta{false}) cases.
%    \begin{macrocode}
\def\@citex[#1][#2]#3{\if@filesw\immediate\write
     \@auxout{\string\citation{#3}}\fi
  \let\@citea\@empty
  \@cite{\let\@citenm\@empty
    \@for\@citeb:=#3\do
    {\def\@tempa##1##2\@nil{\edef\@citeb{\if##1\space##2\else##1##2\fi}}%
     \expandafter\@tempa\@citeb\@nil
     \@ifundefined{b@\@citeb}{\@citea{\reset@font\bfseries ?}\@warning
       {Citation `\@citeb' on page \thepage \space undefined}}%
     {\let\@citemm=\@citenm
     \@cite@parse{\@citeb}%
     \if@tempswa
       \ifx\@citemm\@citenm\@yrsep\else\@citea{\@citenm}\@auyrsep\fi
       \ \@citedt \def\@citea{\@citesep\ }%
     \else
       \ifx\@citemm\@citenm, \@citedt\else\@citea{\@citenm}
           \@citebegin\@citedt\fi
       \def\@citea{\@citeend\@citesep\ }%
     \fi}}\if@tempswa\else\@citeend\fi}{#1}{#2}}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@biblabel}
% \begin{macro}{\@biblabelnum}
% Similarly for the |\@biblabel| command, that is used to format the
% citation label in the list of references, define the author-year version
% as default and then the numerical version. For the former, no labels are
% printed in the list of references.
%    \begin{macrocode}
\def\@biblabel#1{\hfill}
%<*!agu&!nlinproc>
\def\@biblabelnum#1{[#1]}
%</!agu&!nlinproc>
%    \end{macrocode}
% \end{macro}\end{macro}
% 
% \begin{macro}{\@bibsetup}
% \begin{macro}{\@bibsetnum}
% This macro is called by |\thebibliography| and contains any coding for
% formatting the list of references that may be different for numerical and
% author-year schemes. 
% For numerical citations, the |\labelwidth| must be set to the size of the
% longest label (the argument of |\thebibliography|), and the |\leftmargin|
% adjusted accordingly. For author-year, there are no labels, so
% |\labelwidth| is zero, all lines after the first are indented by 1~em.
% 
% Since |\thebibliography| is not included in the \textsl{AGU} package,
% this macro is left off here too.
%    \begin{macrocode}
%<*!agu>
%<*!nlinproc>
\def\@bibsetnum#1{\settowidth\labelwidth{\@biblabel{#1}}%
   \leftmargin\labelwidth \advance\leftmargin\labelsep}
%</!nlinproc>
\def\@bibsetup#1{\leftmargin=1em\itemindent=-\leftmargin}
%</!agu>
%    \end{macrocode}
% \end{macro}\end{macro}
% 
% \subsection{Setting the Defaults}
% \begin{macro}{\ExecuteOptions}
% \changes{5.0}{1994 May 18}{Add \LaTeXe{} options.}
% For \LaTeXe, the defaults (punctuation and scheme type) are set with the
% |\ExecuteOptions| command. For \LaTeX~2.09, the default scheme is
% author-year, and punctuation is set explicitly.
%
% \begin{macro}{\@citebegin}
% \begin{macro}{\@citeend}
% \begin{macro}{\@citesep}
% \begin{macro}{\@auyrsep}
% \begin{macro}{\@yrsep}
% The five punctuation characters for citations are the start and stop
% brackets, the character between multiple citations, the character between
% the authors and year (parenthetical only), and the character between
% adjacent years when the common author list is omitted. Define their
% default values. (\textsl{AGU} uses square braces in place of
% parentheses).
%    \begin{macrocode}
%<*!subpack&209>
\if@twoOnine
%</!subpack&209>
%<*subpack|209>
%<*!agu&!nlinproc>
\def\@citebegin{(} \def\@citeend{)} \def\@citesep{;} 
%</!agu&!nlinproc>
%</subpack|209>
%<*!subpack>
%<*209>
\else
%</209>
\ExecuteOptions{authoryear,round,colon}
\ProcessOptions
%<*209>
\fi
%</209>
%</!subpack>
%<*!agu&!nlinproc>
\def\@auyrsep{,} \def\@yrsep{,}
%</!agu&!nlinproc>
%    \end{macrocode}
% \end{macro}\end{macro}\end{macro}\end{macro}\end{macro}
% \end{macro}
%
% \subsection{Selecting Citation Punctuation and Other Modifications}
% \begin{macro}{\bibstyle}
% The pre-defined punctuation styles are associated with particular
% \texttt{.bst} files. This is implemented by means of the standard
% |\bibliographystyle| command that specifies the name of the \texttt{.bst}
% file that is to be used by \btx. Some \LaTeX{} manuals erroneously state
% that this command must be issued prior to any |\cite| commands. If that
% were the case, the task of invoking the style definitions would be much
% easier, for they certainly must be issued before the first |\cite|.
% However, I have always called |\bibliographystyle| together with
% |\bibliography|, well after all |\cite| commands. 
% 
% In fact, all that |\bibliographystyle{|{\em bst\/}|}| does is to write
% |\bibstyle{|{\em bst\/}|}| to the auxiliary file. This file, and all its
% contents, will be read in at the beginning of the next \LaTeX{} run; to
% be precise, it is read in by |\begin{document}|. The command |\bibstyle| is
% then executed at that point on the next run. However, it is 
% defined to do nothing more than to swallow up its argument! In other
% words, the combination |\bibliographystyle| and |\bibstyle| do absolutely
% nothing to the \LaTeX{} runs. In fact, |\bibstyle| is a command for
% \btx{} alone.
% 
% I have taken advantage of this to redefine |\bibstyle| to execute the
% \texttt{bst}-specific definitions.
%    \begin{macrocode}
%<*!agu&!nlinproc>
\def\bibstyle#1{\@ifundefined{bibstyle@#1}{\relax}
     {\csname bibstyle@#1\endcsname}}
%    \end{macrocode}
% This is executed only when the auxiliary file is read in, and that is
% when |\begin{document}| is issued. Thus this is well before any |\cite|
% commands. It is for this reason that any definitions in the
% |\bibstyle@xxx| commands be global.
% 
% A minor problem arises in that the auxiliary file is read in a second
% time, at the end of the run, to check whether any labels have changed. 
% Sometimes, re-executing the |\bibstyle@xxx| command at this point
% produces error messages. To avoid this, |\bibstyle| is reset to its
% normal, do-nothing, definition after |\begin{document}|.
% 
% \LaTeXe{} provides a better way of adding commands to |\document|,
% which is then exploited here. Paradoxically, the problem with re-reading
% the auxiliary file does not seem to arise for this version.
%    \begin{macrocode}
%<*209>
\if@twoOnine
\let\ori@document=\document
\def\document{\ori@document\global\let\bibstyle=\@gobble}
\else
%</209>
\AtBeginDocument{\global\let\bibstyle=\@gobble}
%<*209>
\fi
%</209>
%</!agu&!nlinproc>
%    \end{macrocode}
% \end{macro}
% 
% \begin{macro}{\bibpunct}
% Now |\bibpunct| is defined. It sets various punctuation commands equal to
% its arguments. It also switches to numerical style if that is specified
% by the fourth argument. This is done by letting |\@bibsetup|,
% |\@citex|, |\@biblabel|, |\@cite| be equal to their numerical 
% counterparts. They are otherwise defined for author-year scheme.
%    \begin{macrocode}
\def\bibpunct#1#2#3#4#5#6{\gdef\@citebegin{#1}\gdef\@citeend{#2}\gdef
   \@citesep{#3}\ifx #4n\global\let\@bibsetup=\@bibsetnum 
   \global\let\@citex=\@citexnum
   \global\let\@biblabel=\@biblabelnum
   \global\let\@cite=\@citenum\fi
   \gdef\@auyrsep{#5}\gdef\@yrsep{#6}}
%    \end{macrocode}
% \end{macro}
% 
% At this point the default punctuation for specific journals may be given,
% now that |\bibpunct| is defined. These will not depend on the
% |\bibliographystyle|, since they should be fixed, even without \btx.
% (The |\bibstyle@xxx| commands are used so that the punctuation is defined
% once and only once in the master file.)
%    \begin{macrocode}
%<agu>\bibstyle@agu
%<nlinproc>\bibstyle@nlinproc
%    \end{macrocode}
% 
% \subsection{The Citations}
% \begin{macro}{\cite}
% \changes{5.0}{1994 May 18}{Add a second optional argument.}
% \begin{macro}{\@citex@}
% \changes{5.0}{1994 May 18}{Add to handle second optional argument.}
% The |\cite| command simply checks if there is an optional argument, and
% then calls |\@citex@|, which in turns checks for a second optional
% then calls the full internal version |\@citex|. The flag |\@tempswa| is
% set \meta{true} if an optional argument is present. I use this to distinguish
% between parenthetical and textual citations.
%    \begin{macrocode}
\def\cite{\@ifnextchar [{\@tempswatrue\@citex@}{\@tempswafalse
    \@citex@[]}}
\def\@citex@[#1]{\@ifnextchar [{\@citex[#1]}{\@citex[][#1]}}
%    \end{macrocode}
% \end{macro}\end{macro}
% 
% \begin{macro}{\citeauthor}
% \changes{5.0}{1994 May 18}{Add means to cite authors only.}
% \begin{macro}{\citeyear}
% \changes{5.0}{1994 May 18}{Add means to cite year only.}
% In an author-year scheme, it is sometimes necessary to refer to the
% authors of a work without the year. It might even be necessary to refer
% to the year alone, but I can hardly imagine that. Both possibilities are
% allowed for here.
%    \begin{macrocode}
\def\citeauthor#1{\ifx\@citex\@citexnum{\reset@font\bfseries(author?)}\@warning
       {Cannot use \string\citeauthor\space with numerical citations}\else
     \@ifundefined{b@#1}{{\reset@font\bfseries ?}\@warning
       {Citation `#1' on page \thepage \space undefined}}%
       {\@cite@parse{#1}\@citenm}\fi}
\def\citeyear#1{\ifx\@citex\@citexnum{\reset@font\bfseries(year?)}\@warning
       {Cannot use \string\citeyear\space with numerical citations}\else
     \@ifundefined{b@#1}{{\reset@font\bfseries ?}\@warning
       {Citation `#1' on page \thepage \space undefined}}%
       {\@cite@parse{#1}\@citedt}\fi}
%    \end{macrocode}
% \end{macro}\end{macro}
% 
% \subsection{Parsing the Author-Year Entries}
% \begin{macro}{\@cite@parse}
% \changes{5.0}{1994 May 18}{Add parsing command, with additional 
%    font and sub-accent commands relaxed.}
% The |\@citex| command takes each entry in its list and parses them
% individually by calling |\@cite@parse|. This is done this by placing the
% decoded text into |\@tempa|, which is used as the argument of |\@citez|,
% which in turn extracts the author and year parts to |\@citenm| and 
% |\@citedt| respectively. 
%    \begin{macrocode}
\def\@cite@parse#1{%
        {\let\prm=\relax\let\psf=\relax\let\ptt=\relax\let\pbf=\relax
        \let\psl=\relax\let\psc=\relax\let\pit=\relax\let\pem=\relax
        \let\prmfamily=\relax\let\psffamily=\relax\let\pttfamily=\relax
        \let\pbfseries=\relax\let\pslshape=\relax\let\pscshape=\relax
        \let\pitshape=\relax\let\pmdseries=\relax\let\pupshape=\relax
        \let\pc=\relax \let\pd=\relax \let\pb=\relax
     \xdef\@tempa{\csname b@#1\endcsname\relax}}%
     \expandafter\@citez\@tempa()\@nil}
%    \end{macrocode}
% Some further notes on the above: it is necessary to turn off all the
% protected font commands |\prm| etc.\ when the label text is expanded into
% |\@tempa|, for otherwise there will be problems with the New Font
% Selection Scheme (NFSS); the protected sub-accent commands (protected
% versions of |\c|, |\d|, and |\b|) also cause troubles on expansion.
% Admittedly, this is not a good solution, for the list of problem commands
% might be much longer, but for the meantime, this will have to do.
% 
% The |\relax| added at the end of the |\@tempa|
% expansion is necessary to serve as a pseudo third argument to
% |\citeauthoryear| for the situation where only two arguments are given
% (see below); the additional |()\@nil| added to the input of |\@citez|
% serves to detect the minimal labelling case of the \texttt{apalike} family.
% \end{macro}
% 
% \begin{macro}{\@citez}
% The author-year information is contained in the \emph{label}, the
% optional argument to |\bibitem|.  To split this label text up into the
% authors and year, the command |\@citez| is used. It expects an argument
% of the form \emph{authors}|(|\emph{year}|)|, so that \emph{authors} is
% argument |#1| and \emph{year} is |#2|. However, if there are no
% parentheses present in the label, they are provided by the calling
% statement (|\@citez\@tempa()\@nil| above) in which case |#2| is blank,
% and the command |\@citeapalk| is invoked instead.
%    \begin{macrocode}
\def\@citez#1(#2)#3\@nil{\gdef\@citenm{#1}\gdef\@citedt{#2}%
%<!all&!apalike&!authordate>}
%<*all|apalike|authordate>
  \if!#2!\expandafter\@citeapalk#1\@nil\fi}
%</all|apalike|authordate>
%    \end{macrocode}
% Note that \texttt{apalike} is only optionally included, with the
% \texttt{docstrip} options \texttt{all} or \texttt{apalike}. It is also 
% included for the \texttt{authordate} system which reduces to \texttt{apalike}.
% \end{macro}
% 
% \subsection{Other Author-Year Schemes}
% \begin{macro}{\@citeapalk}
% \changes{4.1}{1993 Oct 4}{Simplify by using comma-space as separator}
% To parse the label text in an \texttt{apalike} style, we assume that the
% year is separated from the abbreviated author list by means of a comma
% and space. If any other punctuation is used, or if the space if left off,
% or if the comma-space appears anywhere within the author list itself,
% then this will not work correctly.  As I mentioned earlier, the minimal
% \texttt{apalike} citation labelling permits separation of authors and year,
% but in a risky manner.
%    \begin{macrocode}
%<*all|apalike|authordate>
\def\@citeapalk#1, #2\@nil{\gdef\@citenm{#1}\gdef\@citedt{#2}}
%</all|apalike|authordate>
%    \end{macrocode}
% \end{macro}
% 
% The other schemes of citation labelling may also be accommodated, more
% easily than \texttt{apalike}. It is just necessary to define the particular
% commands, like |\citeauthoryear| to format the arguments in the \thestyle{}
% manner, as {\em author\/}|(|{\em year\/}|)|. These commands
% are executed when |\b@|{\em key\/} is expanded into |\@tempa|, so that
% |\@citez| only sees the expansion and never the commands themselves.
% 
% The only complication is that |\citeauthoryear| may be given with two or
% three arguments. This is accommodated by adding |\relax| to the |\@tempa|
% expansion, which becomes the dummy third argument in the two-argument
% case, and otherwise does nothing.
% 
% The Harvard family is allowed for simply by defining |\harvarditem| in
% terms of |\bibitem| with the \thestyle{} labelling form.
% 
% All these are included as optional coding for \texttt{docstrip} such that
% they are present if \thestyle\texttt{.doc} is used in place of 
% \thestyle\texttt{.sty}, but will be missing after a \texttt{docstrip} 
% run without any
% explicit options. The option \texttt{all} includes them all, whereas
% otherwise the options \texttt{harvard}, \texttt{astron}, \texttt{authordate},
% \texttt{newapa}, \texttt{apalike} must be given singly or in combination.
% 
% \begin{macro}{\citeauthoryear}
% For \texttt{newapa.bst} itself, the commands |\citestarts|, |\citeends|,
% as well as 
% |\betweenauthors| must be defined; for others in this group, these
% commands are not needed.
%    \begin{macrocode}
%<*newapa|all>
\def\citeauthoryear#1#2#3{\ifx#3\relax #1(#2)\else #2(#3)\fi}
  \def\citestarts{\@citebegin}
  \def\citeends{\@citeend}
  \def\betweenauthors{and}
%</newapa|all>
%    \end{macrocode}
% \end{macro}
% 
% \begin{macro}{\astroncite}
% The |\astroncite| command is simply defined to produce \thestyle{} 
% format.
%    \begin{macrocode}
%<*astron|all>
\def\astroncite#1#2{#1(#2)}
%</astron|all>
%    \end{macrocode}
% \end{macro}
% 
% \begin{macro}{\citename}
% The |\citename| command just reproduces its argument. Since this is
% in the form |{|{\em authors\/}|, }|{\em year\/}, it has the effect 
% of emulating the \texttt{apalike} style. This is because the |{ }| vanish
% during the expansion.
%    \begin{macrocode}
%<*authordate|all>
\def\citename#1{#1}
%</authordate|all>
%    \end{macrocode}
% \end{macro}
% 
% \begin{macro}{\harvarditem}
% The |\harvarditem| must allow for the optional argument, which is 
% the short author list. Use the short list in |\bibitem| if it is there,
% otherwise the long list must be taken.
%    \begin{macrocode}
%<*harvard|all>
\def\harvarditem{\@ifnextchar[{\@harvarditem}{\@harvarditem[\@empty]}}
\def\@harvarditem[#1]#2#3#4{\if!#1!\bibitem[#2(#3)]{#4}\else
  \bibitem[#1(#3)]{#4}\fi }
%</harvard|all>
%    \end{macrocode}
% \end{macro}
%
% \subsection{The Bibliography Listing}
% Changes must be made to the \texttt{thebibliography} environment for
% author-year citations. This is done be defining the environment with the
% features common to both schemes, and then by invoking |\@bibsetup|, which
% is either the author-year or numerical version.
% 
% \begin{macro}{\bibsection}
% \changes{4.2}{1993 Oct 22}{Make specific for JGR, GRL, NLINPROC}
% First, |\bibsection| is defined according to the main style: if chapters
% exist, then the bibliography is a numberless chapter, otherwise a
% numberless section. For the specific journals, |\bibsection| takes on
% special definitions.
%    \begin{macrocode}
%<*!agu&!nlinproc>
\@ifundefined{chapter}{\def\bibsection{\section*{\refname
   \@mkboth{\uppercase{\refname}}{\uppercase{\refname}}}}}{\def
   \bibsection{\chapter*{\bibname
   \@mkboth{\uppercase{\bibname}}{\uppercase{\bibname}}}}}
%</!agu&!nlinproc>
%<nlinproc>\def\bibsection{\if@draft\newpage\fi
%<nlinproc>    \noappendix\section*{\refname}}
%    \end{macrocode}
% \end{macro}
% 
% \begin{environment}{thebibliography}
% \changes{4.1b}{1993 Oct 18}{Add \cmd{bibfont}, defaulted
%                to \cmd{relax}}
% \changes{4.2}{1993 Oct 22}{Add coding for JGR, GRL, NLINPROC}
% \changes{4.2}{1993 Nov 20}{Remove coding for AGU, since AGU-supplied
%         coding is adequate but different}
% The \texttt{thebibliography} environment is defined much as normal, except
% that |\bibsetup| contains the special features for numerical or
% author-year styles. The command |\bibfont| permits permits different
% font sizes or styles to be used in the list. For example, for 
% \textsl{Nonlinear Processes}. For \textsl{AGU}, the whole
% |\thebibliography| is left off, since the AGU-supplied coding will
% do. It is only necessary to add |\noappendix| to the AGU coding.
%    \begin{macrocode}
%<*!agu>
\def\thebibliography#1{\bibsection\parindent \z@\list
 {\@biblabel{\arabic{enumiv}}}{\@bibsetup{#1}%
    \usecounter{enumiv}\let\p@enumiv\@empty
    \def\theenumiv{\arabic{enumiv}}}%
    \def\newblock{\hskip .11em plus.33em minus.07em}%
    \sloppy\clubpenalty4000\widowpenalty4000
    \sfcode`\.=1000\relax \bibfont}
\let\bibfont=\relax
%<nlinproc>\let\bibfont=\small
%</!agu>
%<agu>\let\aguthebib=\thebibliography
%<agu>\def\thebibliography#1{\noappendix\aguthebib{#1}}
%<*!agu>
\def\endthebibliography{%
  \def\@noitemerr{\@warning{Empty `thebibliography' environment}}%
  \endlist\vskip-\lastskip}
%</!agu>
%    \end{macrocode}
% \end{environment}
% 
% \subsection{Compatibility Commands}
% \begin{macro}{\reset@font}
% For older implementations of \LaTeX~2.09 (before December, 1991) the
% |\reset@font| command does not exist. It is defined to be |\relax| under
% normal \LaTeX{}, but does more under NFSS. In case it is not defined, add
% it here.
%    \begin{macrocode}
%<*209>
\@ifundefined{reset@font}{\let\reset@font=\relax}{}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\bfseries}
% \changes{5.0}{1994 May 18}{Add \LaTeXe{} command for earlier versions.}
% For \LaTeX~2.09, the command |\bfseries| does not exist, so define it as 
% |\bf|. (We want to avoid |\bf| with \LaTeXe{} because it may not always
% exist.)
%    \begin{macrocode}
\@ifundefined{bfseries}{\let\bfseries=\bf}{}
%</209>
%</package>
%    \end{macrocode}
% \end{macro}
%
% \section{The Documentation Driver File}
% The driver file is the actual {\tt.tex} file that outputs the documentation
% that is included in this {\tt.dtx} file. It may be modified to suit
% local conditions or desired output options (see documentation to 
% {\tt doc.sty}).
%    \begin{macrocode}
%<driver&!209>\NeedsTeXFormat{LaTeX2e}
%<driver&!209>\documentclass[a4paper,11pt]{article}
%<driver&!209>\usepackage{doc}
%<driver&!209>\addtolength{\oddsidemargin}{6mm}
%<driver&209>\documentstyle[11pt,a4,doc]{article}
%<driver>\EnableCrossrefs %Comment out when .ind file ready
%<driver>   \DisableCrossrefs %May stay; zapped by \EnableCrossrefs
%<driver>\RecordChanges %Comment out when .gls file ready
%<driver>\CodelineIndex %Comment out when .ind file ready
%<driver>   \CodelineNumbered %May stay
%<driver>%\OnlyDescription
%<driver>
%<driver>\begin{document}
%<driver>   \DocInput{natbib.dtx}
%<driver>   \PrintIndex
%<driver>   \PrintChanges
%<driver>\end{document}
%    \end{macrocode}
% 
% \Finale