forallx.sty

%!TEX root = forallx.tex
\NeedsTeXFormat{LaTeX2e}
\ProvidesPackage{forallx}[2011/10/29 support for a logic textbook]
\RequirePackage{amssymb,hyperref,multicol,ifthen}

% The original forallx.sty was written in 2005

%    ****************************************
%    *            LOGICAL SYMBOLS           *
%    ****************************************
%
% There are, of course, many different symbols used for the truth-functional
% connectives. In order to make the book adaptable, the symbols are defined
% here in the style sheet and these commands are used throughout the book.
% To change conjunction from the ampersand to the carat, for instance,
% change the definition of \eand from ~\&~ to \wedge. To change negation from
% the hoe to the swung dash, change \enot from \neg to {\sim}. Other examples
% are given below.
%
\def\therefore{\ensuremath{\ldotp\dot{}\,\ldotp}}
% disjunction
\def\eor{\ensuremath{\vee}}
% conjunction: 
% {\,^{_{_{_{_{\mbox{\footnotesize\textbullet}}}}}}} gives the dot
\def\eand{\ensuremath{\,\&\,}}
% conditional: \supset gives the horseshoe
\def\eif{\ensuremath{\rightarrow}}
% biconditional: \equiv gives the triple bar
\def\eiff{\ensuremath{\leftrightarrow}}
% negation: {\sim} gives the swung dash 
\def\enot{\ensuremath{\neg}}



%    ****************************************
%    *        TITLE AND VERSION DATA        *
%    ****************************************
% the title of the book
\newcommand*{\forallx}{{\tt forall\script{x}}}
% The version number of the book is a 5 digit integer:
% the last digit of the year, the month, the day of the month
\newcounter{dummy}
\setcounter{dummy}{\year}
\addtocounter{dummy}{-2000}
\newcommand*{\bookversion}{%
	\ifthenelse{\arabic{dummy}<10}{0}{}%
	\arabic{dummy}%
	\ifthenelse{\month<10}{0}{}\number\month%
	\ifthenelse{\day<10}{0}{}\number\day%
}  

% table of contents
\renewcommand{\contentsname}{\forallx\ contents}
% chapter
\usepackage{titlesec}
\titleformat{\chapter}[display]
{\normalfont\bfseries}
{{\titlerule[2pt]}\LARGE Chapter \thechapter}
{1ex}
{\Huge}
[\vspace{1ex}{\titlerule[2pt]}]


%    ****************************************
%    *       SYMBOLS AND SCRIPTY BITS       *
%    ****************************************
% equivalent to commenting something out, but usable on multiple lines
\providecommand{\nix}[1]{}
% script letters are rendered in Zapf Chancery,
% which has both upper and lower case.
\DeclareFontFamily{OT1}{pzc}{}
\DeclareFontShape{OT1}{pzc}{m}{it}{<-> s * [1.200] pzcmi7t}{}
\DeclareMathAlphabet{\mathscr}{OT1}{pzc}{m}{it}
\newcommand*{\script}[1]{\ensuremath{\mathscr{#1}}}
% create a blank
\newcommand*{\blank}{\underline{\hspace*{2.5em}}}
% These are included for discussing formal semantics in predicate logic.
\newcommand*{\model}[1]{\ensuremath{\mathbb{#1}}}
\newcommand*{\extension}[1]{\ensuremath{\mbox{extension}(#1)}}
\newcommand*{\referent}[1]{\ensuremath{\mbox{referent}(#1)}}
  % I personally dislike the default LaTeX angle brackets. I think that
  % they are too narrow. If you want to use them, though, you can
  % replace < and > in the commands below with \langle and \rangle
\newcommand*{\openntuple}{<}
\newcommand*{\closentuple}{>}
\newcommand*{\ntuple}[1]{\mbox{\ensuremath{\mathopen{\openntuple}}#1\ensuremath{\mathclose{\closentuple}}}} 
% definitions
\newcommand*{\define}[1]{\textsc{\lowercase{#1}}}



%    ****************************************
%    *          LIST  ENVIRONMENTS          *
%    ****************************************
% The {earg} environment is used for arguments and example sentences.
% The {ekey} environment is used for symbolization keys.
\newcounter{eargnum}
\newcounter{OLDeargnum}
\newenvironment{earg}%
{\begin{list}{\arabic{eargnum}.}{\usecounter{eargnum}\setlength{\itemsep}{-.4em}}}%
{\setcounter{OLDeargnum}{\arabic{eargnum}}\end{list}}

\newcommand{\ekeylabel}[1]{{\makebox[8ex][r]{\textbf{ #1}}}}
\newenvironment{ekey}{\begin{list}{}{\renewcommand{\makelabel}{\ekeylabel}\setlength{\itemsep}{-.5em}}}{\end{list}}

% Used in conjunction with {earg}, this handles the numbering and
% references to example sentences:
\newcounter{Example}[chapter]
\newcommand*{\ex}[1]{\refstepcounter{Example}\arabic{Example}.\label{#1}}
% Used in specifying partial models, this keeps the lines justified so
% so that the = signs all line up. For example:
%	\begin{partialmodel}
%		UD			& \{Duke, Miles\}\\
%		\extension{B}	& \{Duke\}
%	\end{partialmodel}
\newenvironment{partialmodel}{\par\begin{tabular}{r@{~=~}l}}{\end{tabular}\par}
% define the bullet for {itemize} lists
\renewcommand{\labelitemi}{$\triangleright$}

% \factoidbox{...} produces an inset paragraph of text with a line around it
% Neither for lists nor an environment, but it really didn't
% belong anywhere else.
\newcommand{\factoidbox}[1]{\begin{quote}\framebox{\parbox{\linewidth}{#1}}\end{quote}}

% \tablefbox{...} is used in certain tables to put a box around the contents of specific table cells without having lines that run the whole length of the table
\newcommand{\tablefbox}[1]{\multicolumn{1}{|p{10em}|}{#1}}



%    ****************************************
%    *          PRACTICE PROBLEMS           *
%    ****************************************
\newcounter{ProbPart}
\renewcommand{\theProbPart}{\Alph{ProbPart}}
% This inserts a heading and resets the counter:
\newcommand*{\practiceproblems}{
	\setcounter{ProbPart}{0}\section*{Practice Exercises}%
	\addcontentsline{toc}{section}{Practice Exercises}
}
% This starts a new section which is automatically numbered:
\newcommand*{\problempart}{
	\refstepcounter{ProbPart}\textbf{Part \Alph{ProbPart}}\ 
}
% This bullet is used to indicate that solutions appear at the end of
% the book.
\newcommand*{\solutions}{$\star$}
% When solutions are only given for selected problems, the
% star is placed left of the problem number.
\newcommand*{\leftsolutions}{\hspace{-2.2em}\makebox[2em][l]{\solutions}}

% This is used at the beginning of a section in the solutions
% appendix.
\newcommand*{\solutionsection}[2]{%
	\textbf{\textsc{Chapter {\ref{#1}} Part {\ref{#2}}}}%
	\markright{solutions for ch.~\ref{#1}}%
	\setcounter{countSeq}{0}
}

% This is used to enumerate things that have a given property.
% For example: \nextSeq\nextSeq\noSeq\lastSeq are valid.
% produces   : 1, 2, and 4 are valid.
\newcounter{countSeq}
\newcommand*{\nextSeq}{\stepcounter{countSeq}\arabic{countSeq}, }
\newcommand*{\noSeq}{\stepcounter{countSeq}}
\newcommand*{\lastSeq}{and \stepcounter{countSeq}\arabic{countSeq} }

% This is used to place (eg) a partial model or proof as an item
% in a list. Without it, the item tag will be vertically centered next
% to the model or proof.
%		--- doesn't actually work yet ---
\newenvironment{solutioninlist}{}{}%{~\vspace{-1.6em}}{}


%    ****************************************
%    *         TABLE OF CONTENTS, ETC.      *
%    ****************************************
\setcounter{tocdepth}{1}
\setcounter{secnumdepth}{1}
\renewcommand{\thechapter}{\arabic{chapter}}
\renewcommand{\thesection}{\arabic{chapter}.\arabic{section}}
%\renewcommand{\thesubsection}{\arabic{chapter}.\arabic{section}.\arabic{subsection}}

\renewcommand{\chaptermark}[1]{\markboth%
{\forallx}%
{\textrm{ch.~\thechapter\ \lowercase{#1}}}%
}
\renewcommand{\sectionmark}[1]{}



%    ****************************************
%    *             TRUTH TABLES             *
%    ****************************************

% This facilitates the typesetting of truth tables by
% effectively eliminating the intercolumn space.
% This allows truth tables with the Ts and Fs immediately
% below arbitrary connectives.
% An example follows:
%\begin{center}
%\begin{tabular}{c|c|@{\TTon}*{5}{c}@{\TToff}}
%$A$&$B$&$(A$&\eand&$B)$&\eif&A\\
%\hline
% T & T &    &  T  &    &  T & \\
% T & F &    &  F  &    &  T & \\
% F & T &    &  F  &    &  T & \\
% F & F &    &  T  &    &  T &
%\end{tabular}
%\end{center}

\newcommand*{\TTon}{\hspace{1.5em}\extracolsep{-1em}}
\newcommand*{\TToff}{\extracolsep{-1em}\hspace{.3em}}
\newcommand*{\TTbf}[1]{\textbf{\large #1}}



%    ****************************************
%    *                PROOFS                *
%    ****************************************

% based on fitch.sty by Peter Selinger, University of Ottawa
% v 0.4, (C) 2002 Peter Selinger
% revised 2003--5 by P.D. Magnus

% Selinger released this code under the GNU General Public License,
% version 2 or later. So this bit of the style is free to you under
% the GPL.

% ----------------------------------------------------------------------
% The comments in this file are intended for programmers who
% might want to hack this package. For information on how to use the
% package, the file fitchdoc.tex is a better place to look.
% ----------------------------------------------------------------------

% Global identifiers defined by this package start with '\nd*'. The
% only exceptions are \ndref, \nddim, and the "nd" and "ndresume"
% latex environments.

{\chardef\x=\catcode`\*
\catcode`\*=11
\global\let\nd*astcode\x}
\catcode`\*=11

% The macros provided by this package mix TeX and LaTeX primitives.
% LaTeX is used for \rule, \settowidth, \addtolength, \hspace...
% All macros are assumed to be called in math mode.

% Translation proceeds through several layers of macros. Each layer
% consist of macros which expand into macros of the previous
% layer. Each layer may have some global state and initialization
% functions. Only the topmost layer (layer C) is directly
% user-accessible. 


% References

% We start with some macros to facilitate automatic line numbering, and
% for referencing of lines by labels. The macros defined here are:
% \nd*reset to reset the line number count. \nd*num{x}, to generate the next
% line number and store it in reference x; \nd*ref{x} to print the line
% number referenced by x, \ndref{xxx} to parse a list of references,
% separated by commas, periods, and hyphens, and translate all references to
% line numbers. Note: \ndref ignores spaces in its argument, but puts
% a space after each comma or period in the output. Also note: \nd*ref can be
% useful outside a natded environment, and thus it has a user
% accessible name. Most general ``line numbers'' actually consist of a
% name (such as ``n'') and a number (such as ``2''), to produce output
% such as $n+2$. \nd*set{n}{m} is called to set the letter to n and
% the number to m. As special cases, if the second argument is empty,
% it is not set, and if the first argument is \relax, it is not set.

% Example for references:

% \nd*reset \nd*num{x}; \nd*num{y}; \nd*numopt{n+1}{z}; \nd*num{zz}; 
% \nd*ref{y}; \ndref{x, y-zz, z}
% will produce: 1; 2; n+1; 3; 2; 1, 2-3, n+1

\newcount\nd*ctr
\def\nd*render{\expandafter\ifx\expandafter\nd*x\nd*base\nd*x\the\nd*ctr\else\nd*base\ifnum\nd*ctr<0\the\nd*ctr\else\ifnum\nd*ctr>0+\the\nd*ctr\fi\fi\fi}
\expandafter\def\csname nd*-\endcsname{}

%\def\nd*num#1{\global\advance\nd*ctr1\nd*numo{\the\nd*ctr}{#1}}
\def\nd*num#1{\nd*numo{\nd*render}{#1}\global\advance\nd*ctr1}
\def\nd*numopt#1#2{\nd*numo{$#1$}{#2}}
\def\nd*numo#1#2{\edef\x{#1}\mbox{$\x$}\expandafter\global\expandafter\let\csname nd*-#2\endcsname\x}
\def\nd*ref#1{\expandafter\let\expandafter\x\csname nd*-#1\endcsname\ifx\x\relax%
  \errmessage{Undefined natdeduction reference: #1}\else\mbox{$\x$}\fi}
\def\nd*noop{}
\def\nd*set#1#2{\ifx\relax#1\nd*noop\else\global\def\nd*base{#1}\fi\ifx\relax#2\relax\else\global\nd*ctr=#2\fi}
\def\nd*reset{\nd*set{}{1}}
\def\nd*refa#1{\nd*ref{#1}}
\def\nd*aux#1#2{\ifx#2-\nd*refa{#1}--\def\c{\nd*aux{}}%
  \else\ifx#2,\nd*refa{#1}, \def\c{\nd*aux{}}%
  \else\ifx#2;\nd*refa{#1}; \def\c{\nd*aux{}}%
  \else\ifx#2.\nd*refa{#1}. \def\c{\nd*aux{}}%
  \else\ifx#2)\nd*refa{#1})\def\c{\nd*aux{}}%
  \else\ifx#2(\nd*refa{#1}(\def\c{\nd*aux{}}%
  \else\ifx#2\nd*end\nd*refa{#1}\def\c{}%
  \else\def\c{\nd*aux{#1#2}}%
  \fi\fi\fi\fi\fi\fi\fi\c}
\def\ndref#1{\nd*aux{}#1\nd*end}


% Layer A

% Layer A provides primitive picture elements which can be combined
% into natural deduction derivations. These are: \nd*t to make a
% topmost vertical line segment; \nd*v to make a continuation vertical
% line segment, \nd*i to produce the indentation for a subproof,
% \nd*s to produce the horizontal space between a vertical line and a
% formula, \nd*u{x} to underline x with appropriate spacing for a
% hypothesis. \nd*f{x} typesets the formula x with the appropriate vertical
% spacing. \nd*g{x} is like \nd*i, except it puts a guard in the
% space it creates. These elements are spaced so that they are appropriate
% as left-aligned array entries. Line numberings and justifications
% must be provided manually in this layer. All explicit spacing
% information is contained in this layer; higher layers manipulate only
% layer A primitives.

% define various dimensions (explained in fitchdoc.tex):
\newlength{\nd*dim} 
\newdimen\nd*depthdim
\newdimen\nd*hsep
% user command to redefine dimensions
\def\nddim#1#2#3#4#5#6#7#8{\nd*depthdim=#3\relax\nd*hsep=#6\relax%
\def\nd*height{#1}\def\nd*thickness{#8}\def\nd*initheight{#2}%
\def\nd*indent{#5}\def\nd*labelsep{#4}\def\nd*justsep{#7}}
% set initial dimensions
\nddim{4.5ex}{3.5ex}{1.5ex}{1em}{1.6em}{.5em}{2.5em}{.2mm}

\def\nd*v{\rule[-\nd*depthdim]{\nd*thickness}{\nd*height}}
\def\nd*t{\rule[-\nd*depthdim]{0mm}{\nd*height}\rule[-\nd*depthdim]{\nd*thickness}{\nd*initheight}}
\def\nd*i{\hspace{\nd*indent}} 
\def\nd*s{\hspace{\nd*hsep}}
\def\nd*g#1{\nd*f{\makebox[\nd*indent][c]{$#1$}}}
\def\nd*f#1{\raisebox{0pt}[0pt][0pt]{$#1$}}
\def\nd*u#1{\makebox[0pt][l]{\settowidth{\nd*dim}{\nd*f{#1}}%
    \addtolength{\nd*dim}{2\nd*hsep}\hspace{-\nd*hsep}\rule[-\nd*depthdim]{\nd*dim}{\nd*thickness}}\nd*f{#1}}

% Example of a derivation using layer A syntax:

%\begin{array}{lll}
%  1  &  \nd*t\nd*s\nd*f            {P\vee Q}                           \\
%  2  &  \nd*v\nd*s\nd*u            {\neg Q}                            \\
%  3  &  \nd*v\nd*i\nd*t\nd*s\nd*u  {P}                                 \\
%  4  &  \nd*v\nd*i\nd*v\nd*s\nd*f  {P}       &  \mbox{by 3}            \\
%  5  &  \nd*v\nd*i\nd*t\nd*s\nd*u  {Q}                                 \\
%  6  &  \nd*v\nd*i\nd*v\nd*s\nd*f  {\neg Q}  &  \mbox{by 2}            \\
%  7  &  \nd*v\nd*i\nd*v\nd*s\nd*f  {\bot}    &  \mbox{by 5, 6}         \\
%  8  &  \nd*v\nd*i\nd*v\nd*s\nd*f  {P}       &  \mbox{by 7}            \\
%  9  &  \nd*v\nd*s\nd*f            {P}       &  \mbox{by 1, 3-4, 5-8}  \\
%\end{array}


% Lists

% This is a bit of a hack. We implement linked lists as follows: a
% list is either \nd*nil, or \nd*cons{T}{H}, where T is another list,
% and H is some arbitrary code. Note that lists grow to the right. 
% The following macros operate on a list that is stored in a macro
% \list. 
% \nd*push\list{item} pushes the item onto the list
% \nd*pop\list{item} pops and discards the last item from the list
% \nd*item\list{command} applies command to each element of the list
% \nd*modify\list\n{elt} modifies the \n-th element of the
% list, if there is such an element. Here \n is a counter. Elements
% are counted from the right, starting from 1.

\def\nd*push#1#2{\expandafter\gdef\expandafter#1\expandafter%
  {\expandafter\nd*cons\expandafter{#1}{#2}}}
\def\nd*pop#1{{\def\nd*nil{\gdef#1{\nd*nil}}\def\nd*cons##1##2%
    {\gdef#1{##1}}#1}}
\def\nd*iter#1#2{{\def\nd*nil{}\def\nd*cons##1##2{##1#2{##2}}#1}}
\def\nd*modify#1#2#3{{\def\nd*nil{\gdef#1{\nd*nil}}\def\nd*cons##1##2%
    {\advance#2-1 ##1\advance#2 1 \ifnum#2=1\nd*push#1{#3}\else%
      \nd*push#1{##2}\fi}#1}}

% we use lists of items of the forms \nd*t, \nd*v, \nd*i, and
% \nd*g{...} to represent the current indentation level and
% format (see Layer A, above). The following function 
% computes the indentation for the following line by replacing all
% items of the form \nd*t by \nd*v and \nd*g{...} by \nd*i. 

\def\nd*cont#1{{\def\nd*t{\nd*v}\def\nd*v{\nd*v}\def\nd*g##1{\nd*i}%
    \def\nd*i{\nd*i}\def\nd*nil{\gdef#1{\nd*nil}}\def\nd*cons##1##2%
    {##1\expandafter\nd*push\expandafter#1\expandafter{##2}}#1}}

% With the list syntax, a derivation can be expressed like this:

% \[\begin{array}{lll}
%   \gdef\stack{\nd*nil}
%   \newcount\n
%   \nd*push\stack{\nd*t}
%   1 & \nd*iter\stack\relax\nd*s\nd*u       {\neg\exists xP(x)} \\
%   \nd*cont\stack
%   \nd*push\stack{\nd*i}
%   \nd*push\stack{\nd*t}
%   \nd*n=2\nd*modify\stack\n{\nd*g{u}}
%   \nd*push\stack{\nd*i}
%   \nd*push\stack{\nd*t}
%   2 & \nd*iter\stack\relax\nd*s\nd*u       {P(u)} \\
%   \nd*cont\stack
%   3 & \nd*iter\stack\relax\nd*s\nd*f       {\exists xP(x)} \\
%   \nd*cont\stack
%   4 & \nd*iter\stack\relax\nd*s\nd*f       {\neg\exists xP(x)} \\
%   \nd*cont\stack
%   5 & \nd*iter\stack\relax\nd*s\nd*f       {\bot} \\
%   \nd*cont\stack
%   \nd*pop\stack
%   \nd*pop\stack
%   6 & \nd*iter\stack\relax\nd*s\nd*f       {\neg P(u)} \\
%   \nd*cont\stack
%   \nd*pop\stack
%   \nd*pop\stack
%   7 & \nd*iter\stack\relax\nd*s\nd*f       {\forall y\neg P(y)} \\
%   \nd*cont\stack
%  \end{array}
% \]


% Layer B

% Layer B is simply a wrapper around layer A. It provides commands
% \nd*beginb, \nd*resumeb, \nd*endb, \nd*openb, \nd*closeb,
% \nd*guardb, \nd*hypob, and \nd*haveb which abstract from the layer A 
% primitives. This includes automatic line numbering, and automatic
% indentation. \nd*beginb and \nd*endb enclose a natural deduction in
% layer B syntax. \nd*resumeb is like \nd*beginb, except that it
% resumes a deduction in progress (for instance, after a manual page
% break). \nd*openb and \nd*closeb open, respectively close, a
% subproof.  \nd*guardb{n}{g} adds the guard g to the nth enclosing
% subderivation (counted from 1 from the inside). \nd*hypob 
% introduces a hypothesis, and \nd*haveb introduces a non-hypothesis
% line in a proof.  Line numbering is integrated, but justifications
% must still be given manually. Also, proof lines must still be
% terminated by '\\'. An idiosyncracy of this layer is that in a list
% of several hypotheses, all but the last one must be called with
% \nd*haveb, not \nd*hypob, to avoid drawing a horizontal line under
% each of them.

\newcount\nd*n
\def\nd*beginb{\begingroup\nd*reset\gdef\nd*stack{\nd*nil}\nd*push\nd*stack{\nd*t}%
  \begin{array}{l@{\hspace{\nd*labelsep}}l@{\hspace{\nd*justsep}}l}}
\def\nd*resumeb{\begingroup\begin{array}{r@{\hspace{\nd*labelsep}}l@{\hspace{\nd*justsep}}l}}
\def\nd*endb{\end{array}\endgroup}
\def\nd*hypob#1#2{\nd*f{\nd*num{#1}}&\nd*iter\nd*stack\relax\nd*cont\nd*stack\nd*s\nd*u{#2}&}
\def\nd*haveb#1#2{\nd*f{\nd*num{#1}}&\nd*iter\nd*stack\relax\nd*cont\nd*stack\nd*s\nd*f{#2}&}
\def\nd*openb{\nd*push\nd*stack{\nd*i}\nd*push\nd*stack{\nd*t}}
\def\nd*closeb{\nd*pop\nd*stack\nd*pop\nd*stack}
\def\nd*guardb#1#2{\nd*n=#1\multiply\nd*n by 2 \nd*modify\nd*stack\nd*n{\nd*g{#2}}}

% Example of a derivation using layer B syntax. Note that the "line
% numbers" are really labels, which will be replaced by consecutive
% line numbers in the output.

% \[
%   \nd*beginb
%   \nd*haveb  {1}{P\vee Q}                               \\
%   \nd*hypob  {2}{\neg Q}                                \\
%   \nd*openb
%   \nd*hypob  {3}{P}                                     \\
%   \nd*haveb  {4}{P}       \mbox{by \ndref{3}}           \\
%   \nd*closeb
%   \nd*openb
%   \nd*hypob  {5}{Q}                                     \\
%   \nd*haveb  {6}{\neg Q}  \mbox{by \ndref{2}}           \\
%   \nd*haveb  {6a}{\bot}   \mbox{by \ndref{5,6}}         \\
%   \nd*haveb  {6b}{P}      \mbox{by \ndref{6a}}          \\
%   \nd*closeb
%   \nd*haveb  {8}{P}       \mbox{by \ndref{1,3-4,5-6b}}  \\
%   \nd*endb
% \]

% Here is another example, using a guard.

% \[
%   \nd*beginb
%   \nd*hypob  {1}{\neg\exists xP(x)}   \\
%   \nd*openb
%   \nd*guardb {1}{u}
%   \nd*openb
%   \nd*hypob  {2}{P(u)}                \\
%   \nd*haveb  {3}{\exists xP(x)}       \mbox{by \ndref{2}}  \\
%   \nd*haveb  {4}{\neg\exists xP(x)}   \mbox{by \ndref{1}}  \\
%   \nd*haveb  {5}{\bot}                \mbox{by \ndref{3,4}}\\
%   \nd*closeb
%   \nd*haveb  {6}{\neg P(u)}           \mbox{by \ndref{2-5}}\\
%   \nd*closeb
%   \nd*haveb  {7}{\forall y\neg P(y)}  \mbox{by \ndref{2-6}}\\
%   \nd*endb
% \]


% Layer C

% Layer C is the syntax used by the end user. It is implemented as a
% wrapper around layer B, providing six additional conveniences: 
% (1) no more need for explicit '\\', (2) all hypotheses 
% are denoted \hypo, (3) a convenient syntax for writing justification
% labels, (4) a latex environment, (5) guard as optional argument to
% \have, \hypo, or \open, (6) optional relabeling arguments. The user
% level commands are similar to those of layer B: they are called
% \begin{nd}, \end{nd}, \open, \close, \hypo, \have. In addition there
% is a \by command for writing justification labels, in the style of
% \by{$\vee$E}{1,2-4,5-6}. For convenience, a number of abbreviations
% is also provided, for instance \ie for \by{$\Rightarrow$E}
% etc. These commands are only visible inside an nd-environment; thus
% they do not interfere with the global name space. There is also an
% environment ndresume which is like nd, except that it continues a
% proof in progress (with continuous nesting and labeling).

% The layer C macros work by storing each line in a data structure
% \ppp,\nd*typ,\nd*byt. The line is ejected when the beginning of the next
% line is read, and once at the very end. In this way, we can put in
% the correct line breaks (whether or not the line carries a
% justification), and a hypothesis does not get typeset until we know
% whether it is followed by another hypothesis. \nd*sto stores a new
% line, \nd*clr clears the current line, \nd*cmd outputs the current
% line. Finally, \nd*init puts all the commands which are visible
% inside an nd-environment in the current name space.

\def\nd*clr{\gdef\nd*cmd{}}
\def\nd*sto#1#2#3{\gdef\nd*typ{#1}\gdef\nd*byt{}%
  \gdef\nd*cmd{\nd*typ{#2}{#3}\nd*byt\\}}
\def\nd*hyc#1#2{\def\nd*typ{\nd*haveb}\nd*cmd\nd*sto{\nd*hypob}{#1}{#2}}
\def\nd*hac#1#2{\nd*cmd\nd*sto{\nd*haveb}{#1}{#2}}

% usage: \optarg{default}{continuation}xxx - reads an optional argument, 
% supplies default if necessary, then continues with continuation. 
% Continuation expects optional argument between [...]. I.e., 
% \optarg{d}{c}[xxx] => c[xxx], and \optarg{d}{c}x => c[d]x if x != '['. 
% Behavior is undefined if x is {[...}. \optargg is similar except it 
% takes two continuations: first one for optional argument present, second 
% for not present. It takes no default value.

\def\optarg#1#2#3{\ifx[#3\def\c{#2#3}\else\def\c{#2[#1]{#3}}\fi\c}
\def\optargg#1#2#3{\ifx[#3\def\c{#1#3}\else\def\c{#2{#3}}\fi\c}

\def\nd*hyx[#1][#2]#3[#4]#5{\ifx\relax#4\relax\else\nd*guardb{1}{#4}\fi\nd*hyc{#3}{#5}\nd*set{#1}{#2}}
\def\nd*hax[#1][#2]#3[#4]#5{\ifx\relax#4\relax\else\nd*guardb{1}{#4}\fi\nd*hac{#3}{#5}\nd*set{#1}{#2}}

% \nd*five{\a}: read five, partly optional arguments of the shape [][]{}[]{}, 
% then call \a with these arguments.
\def\nd*five#1{\optargg{\nd*four{#1}}{\nd*two{#1}}}
\def\nd*four#1[#2]{\optarg{0}{\nd*three{#1}[#2]}}
\def\nd*three#1[#2][#3]#4{\optarg{}{#1[#2][#3]{#4}}}
\def\nd*two#1{\nd*three{#1}[\relax][]}

\def\nd*have{\nd*five{\nd*hax}}
\def\nd*hypo{\nd*five{\nd*hyx}}
\def\nd*base{undefined}

\def\nd*open{\optargg{\nd*openopt}{\nd*opennoopt}}
\def\nd*openopt[#1]{\nd*cmd\nd*clr\nd*openb\nd*guard{#1}}
\def\nd*opennoopt#1{\nd*cmd\nd*clr\nd*openb#1}
\def\nd*close{\nd*cmd\nd*clr\nd*closeb}
\def\nd*guard{\optarg{1}{\nd*guardc}}
\def\nd*guardc[#1]#2{\nd*guardb{#1}{#2}}

\def\nd*by#1#2{\ifx\nd*x#2\nd*x\gdef\nd*byt{\mbox{#1}}\else\gdef\nd*byt{\mbox{#1\ \ndref{#2}}}\fi}

% * * *
% This block defines the natural deduction rules.
% Rules designated by ordinary letters may be specified with \by{RULE}
% * * *

\def\nd*init{%
  \let\open\nd*open%
  \let\close\nd*close%
  \let\hypo\nd*hypo%
  \let\have\nd*have%
  \let\by\nd*by%
  \let\guard\nd*guard%
  \def\bi{\by{{\eiff}I}}%
  \def\be{\by{{\eiff}E}}%
  \def\ci{\by{{\eif}I}}%
  \def\ce{\by{{\eif}E}}%
  \def\Ai{\by{$\forall$I}}%
  \def\Ae{\by{$\forall$E}}%
  \def\Ei{\by{$\exists$I}}%
  \def\Ee{\by{$\exists$E}}%
  \def\ae{\by{{\eand}E}}%
  \def\ai{\by{{\eand}I}}%
  \def\oi{\by{{\eor}I}}%
  \def\oe{\by{{\eor}E}}%
  \def\ni{\by{{\enot}I}}%
  \def\ne{\by{{\enot}E}}%
  \def\ii{\by{$=$I}}%
  \def\ie{\by{$=$E}}%
}
\newenvironment{nd}{\begingroup\nd*init\nd*beginb\nd*clr}{\nd*cmd\nd*endb\endgroup}
\newenvironment{ndresume}{\begingroup\nd*init\nd*resumeb\nd*clr}%
  {\nd*cmd\nd*endb\endgroup}

% Example of a derivation using layer C syntax. As before, the "line
% numbers" are really labels, which will be replaced by consecutive
% line numbers in the output.

% \[
% \begin{nd}
%   \hypo{1}  {P\vee Q}   
%   \hypo{2}  {\neg Q}                         
%   \open                              
%   \hypo{3a} {P}
%   \have{3b} {P}        \r{3a}
%   \close                   
%   \open
%   \hypo{4a} {Q}
%   \have{4b} {\neg Q}   \r{2}
%   \have{4c} {\bot}     \ne{4a,4b}
%   \have{4d} {P}        \be{4c}
%   \close                             
%   \have{5}  {P}        \oe{1,3a-3b,4a-4d}                 
% \end{nd}
% \]

% Another example of layer C syntax, using guards and relabelings:

% \begin{nd}
%   \hypo          {1} {P\vee Q}
%   \open
%   \hypo          {2}[u] {P}
%   \have [\vdots] {3} {\vdots}
%   \have [n][-1]  {4} {A\wedge B}
%   \close
%   \open
%   \hypo          {5} {Q}
%   \have [\vdots] {6} {\vdots}
%   \have [m]      {7} {A\wedge B}
%   \close
%   \have          {8} {A\wedge B}  \oe{1,2-(4),5-7}
%   \have [\vdots] {9} {\vdots}
%   \have [][100] {10} {A}          \ae{8}
% \end{nd}

\catcode`\*=\nd*astcode

% a command for indicating the goal in a proof or subproof
\newcommand*{\want}[1]{\by{want \ensuremath{#1}}{}}
% an environment that separates the proof from surrounding paragraphs
\newenvironment{proof}{\par$\begin{nd}}{\end{nd}$\par}

% I keep mixing up the \ce and \ae commands, so I define a less ambiguous
% alternate set of commands

\newcommand*{\notI}{\ni}
\newcommand*{\notE}{\ne}
\newcommand*{\iffI}{\bi}
\newcommand*{\iffE}{\be}
\newcommand*{\ifI}{\ci}
\newcommand*{\ifE}{\ce}
\newcommand*{\andI}{\ai}
\newcommand*{\andE}{\ae}
\newcommand*{\orI}{\oi}
\newcommand*{\orE}{\oe}
\newcommand*{\forallI}{\Ai}
\newcommand*{\forallE}{\Ae}
\newcommand*{\existsI}{\Ei}
\newcommand*{\existsE}{\Ee}