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authorKarl Berry <karl@freefriends.org>2016-03-01 23:30:12 +0000
committerKarl Berry <karl@freefriends.org>2016-03-01 23:30:12 +0000
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-%%% ====================================================================
-%%% @LaTeX-file{
-%%% filename = "technote.tex",
-%%% version = "2.0",
-%%% date = "1999/11/15",
-%%% time = "15:07:20 EST",
-%%% checksum = "58506 233 1647 12005",
-%%% author = "American Mathematical Society",
-%%% copyright = "Copyright 1995, 1999 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,
-%%% Technical Support,
-%%% Electronic Products and Services,
-%%% P. O. Box 6248,
-%%% Providence, RI 02940,
-%%% USA",
-%%% telephone = "401-455-4080 or (in the USA and Canada)
-%%% 800-321-4AMS (321-4267)",
-%%% FAX = "401-331-3842",
-%%% email = "tech-support@ams.org (Internet)",
-%%% supported = "yes",
-%%% keywords = "amsmath, latex",
-%%% abstract = "This is part of the AMS-\LaTeX{} distribution. It
-%%% is a document discussing some technical issues in the
-%%% contents and interface of AMS-\LaTeX{} packages."
-%%% 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.",
-%%% }
-%%% ====================================================================
-\NeedsTeXFormat{LaTeX2e}% LaTeX 2.09 can't be used (nor non-LaTeX)
-[1994/12/01]% LaTeX date must December 1994 or later
-\documentclass{amsdtx}
-
-\title{Technical notes on the \pkg{amsmath} package}
-\author{American Mathematical Society\\Michael Downes}
-\date{1999/10/29}
-
-\markboth
- {Technical notes on the \pkg{amsmath} package}
- {Technical notes on the \pkg{amsmath} package}
-\renewcommand{\sectionmark}[1]{}
-
-\providecommand{\etc}[1]{etc.}
-
-\providecommand{\begend}[1]{%
- {\ntt \symbol{92}begin\symbol{123}#1\symbol{125}}
- \ldots\ {\ntt\symbol{92}end\symbol{123}#1\symbol{125}}%
-}
-
-\MakeShortVerb{\|}
-
-\begin{document}
-\maketitle
-
-\section{Introduction}
-
-These notes are miscellaneous remarks on some technical questions
-applicable to version 2.0 of \amslatex/.
-
-\section{Deprecated and disallowed commands}
-
-Certain commands that were in the \pkg{amstex} package (the predecessor,
-in \amslatex/ 1.0 and 1.1, of the \pkg{amsmath} package) were moved into
-\pkg{amsxtra} because they seemed to be little-used relics:
-\cn{accentedsymbol}, \qq{sup accents} (\cn{sptilde}, \cn{sphat}, etc.).
-
-Certain other commands\mdash e.g., \cn{over}, \cn{pmatrix}, and
-\cn{cases}\mdash are changed by the \pkg{amsmath} package to produce
-warning messages or error messages, depending on their history; these
-are discussed in more detail in the following sections.
-
-\section{Why do \cn{matrix}, \cn{pmatrix}, and \cn{cases} stop working
-when I add the \pkg{amsmath} package?}
-
-If you used the \fn{plain.tex} versions of \cn{matrix}, \cn{pmatrix}, or
-\cn{cases} in a document and then later converted the document to use
-the \pkg{amsmath} package (or one of the AMS documentclasses, which
-automatically call the \pkg{amsmath} package internally), the instances
-of those commands will produce error messages. The problem is that when
-\latex/ was originally created, it adopted most of its mathematics
-features straight from \fn{plain.tex}. But in the case of \cn{matrix},
-\cn{pmatrix}, \cn{cases} this was a mistake\mdash the \fn{plain.tex}
-syntax for them is decidedly non-\latex/ in style, for example the fact
-that they use \cs{cr} instead of \cn{\\} to mark line breaks, and they
-don't use \cn{begin} and \cn{end}. In basic \latex/ this mistake will be
-perpetuated at least until \latex/3 appears, in order to avoid breaking
-existing documents. But no existing documents that were written with the
-\pkg{amsmath} package have that syntactic problem, as \pkg{amsmath}
-provides proper \latex/-syntax versions of \cn{matrix} and the others.
-The possibility of optionally allowing the \fn{plain.tex} variants to
-make document conversion easier seems ill-advised since those variants
-are so blatantly wrong in a \latex/ context. The \env{array} environment
-ought to have been used instead.
-
-\section{Why do \cn{over}, \cn{atop}, \cn{above} [\dots{\ntt withdelims}]
- give a warning when I add the \pkg{amsmath} package?}
-
-Using the six generalized fraction commands \cn{over},
-\cn{overwithdelims}, \cn{atop}, \cn{atopwithdelims}, \cn{above},
-\cn{abovewithdelims} is not really a good idea in \latex/, for reasons
-explained below. I construe \latex/'s provision of \cs{frac}, and the
-lack of any mention in the \latex/ book of the primitive fraction
-commands, as an implicit injunction against their use, although I don't
-think Lamport actually spent a lot of time pondering the issue, and the
-basic \latex/ version of \cn{frac} provides access only to \cn{over},
-not to \cn{atop}, \cn{above}, or the \verb'withdelims' variants. The
-\pkg{amsmath} package, however, provides a \cn{genfrac} command that
-gives user-level access to all six of the generalized fraction
-primitives in a way that conforms to the syntactic conventions followed
-by all other \latex/ commands.
-
-Not only is the unusual syntax of the \tex/ primitives rather out of
-place in \latex/, but furthermore that syntax seems to be responsible
-for one of the most significant flaws in \tex/'s mathematical
-typesetting capabilities: the fact that the current mathstyle at any
-given point in a math formula cannot be determined until the end of the
-formula, because of the possibility that a following generalized
-fraction command will change the mathstyle of the \emph{preceding}
-material. To cite two of the worst side effects: \cn{mathchoice} must
-actually typeset all four of its arguments, instead of being able to
-immediately select only one; and, were it possible to always know the
-current math style at a given point, math font selection would be
-greatly simplified and the upper limit of 16 different math font
-\cn{fam}s would never be a problem as \cn{text,script[script]font}
-assignments for any \cn{fam} could take immediate effect and therefore
-could be changed arbitrarily often within a single formula. More
-concretely, math font selection difficulties are responsible for many of
-the more convoluted passages in the source code of \latex/'s NFSS (that
-does font loading on demand) and of the \pkg{amsmath} package, and by
-extension it has historically been responsible for significant delays in
-making new features available to end users and for making those features
-more prone to bugs.
-
-There are additional bad consequences following from the syntax of those
-generalized fraction commands that only become evident when you do some
-writing of nontrivial macros for math use. For example, as things
-currently stand you cannot measure the size of any object in math
-without going through \cn{mathchoice} and \emph{leaving and reentering
-math mode} via \verb'\hbox{$' (which then introduces complications
-regarding \cn{everymath} and \cn{mathsurround}). And it seems that
-uncertainty about the current mathstyle is the only barrier to allowing
-the use of mu units with \cn{vrule}, to make vertical struts in
-constructing compound symbols or notation. And so on and so forth.
-
-\section{The \opt{fleqn} option and \cn{mathindent}}
-
-Strictly speaking, the \pkg{amsmath} package doesn't use \cn{mathindent}
-to control the left indent of displayed equations when the \opt{fleqn}
-option is in effect: it uses an internal parameter \cs{@mathmargin}
-instead. However, for compatibility with existing \latex/ documentation,
-\pkg{amsmath} turns \cn{mathindent} into an alias for \cs{@mathmargin}.
-There is a small risk here: In the plain \latex/ implementation,
-\cn{mathindent} is a dimen register, but with \pkg{amsmath}
-\cs{@mathmargin} is a skip register and, by association, so is
-\cn{mathindent}. If any package or documentclass uses \cn{mathindent} in
-a way that depends on it being a dimen register, when used in
-conjunction with the \pkg{amsmath} package it may be vulnerable to a
-well-known pitfall having to do with the primitive \tex/ lookahead for a
-\texttt{plus} or \texttt{minus} key word. However if the standard
-\latex/ commands \cn{setlength} and \cn{addtolength} are used to modify
-\cn{mathindent} then this problem will not arise.
-
-\section{Why can't I use abbreviations for \protect\begend{align}?}
-
-Authors often like to use abbreviations such as |\beq| |\eeq| for
-|\begin{equation}| |\end{equation}|. For some environments defined by
-the \pkg{amsmath} package, such as \env{align}, \env{gather},
-\env{multline}, and others of the same general type, this does not work:
-An attempt to define |\bal| |\eal| as shorthand for |\begin{align}|
-|\end{align}| will fail with a puzzling error message. This has to do
-with unfortunately nontrivial technical complications: the given
-environments must read their contents as a delimited macro argument
-because they do multipass processing of the contents using algorithms
-inherited from Spivak's \fn{amstex.tex}. The obvious
-solution\mdash substitution of different algorithms that do box shuffling
-instead of token shuffling for the multipass calculations\mdash would
-require rewriting these display environments from the ground up; while
-that is a worthy goal, it was beyond the original scope of the
-\amslatex/ project. Work is under way on an auxiliary package called
-\pkg{breqn} that addresses not only this problem but a number of others;
-at the time of this writing, however [September 1999] it has only
-progressed as far as a beta release.
-
-Some workarounds:
-\begin{itemize}
-\item |\def\bal#1\eal{\begin{align}#1\end{align}}|
-\item Define |\newcommand{\env}[2]{\begin{#1}#2\end{#1}}| and then use
- |\env{align}{...}|
-\end{itemize}
-
-\section{The \pkg{upref} package}
-
-The reason for splitting out the \pkg{upref} package instead of
-automatically incorporating it in the \cls{amsart} and \cls{amsbook}
-classes is this: It involves low-level surgery on an important \latex/
-command. This means that if ever this command changes in the future (as
-it did between versions 2.09 and 2e of \latex/) we have a maintenance
-problem. And the benefit that \pkg{upref} provides is something that
-most end users don't care much about.
-
-\section{The \pkg{amsintx} package}
-
-After a very preliminary trial release the \pkg{amsintx} package was
-withdrawn to await further development. It is still considered a worthy
-project but has simply not yet made it to the head of the priority queue
-in the AMS \latex/ development program, as it has had to contend with a
-number of other equally worthy projects for development time.
-
-\section{Hyphenation in the documentation}
-
-Hyphenation was allowed for certain long command names in
-\fn{amsldoc.tex}; this presented technical difficulties because \latex/
-normally deactivates hyphenation for tt fonts. The method chosen to
-reinstate hyphenation was to turn off the encoding-specific function
-\cs{OT1+cmtt} that disables the \cs{hyphenchar} for tt fonts; see the
-definition of \cn{allowtthyphens} in \fn{amsdtx.dtx}. Then a list of all
-tt words in the document was gathered (from the \fn{.idx} file, produced
-by the \cn{cn}, \cn{fn}, \cn{pkg}, etc. commands) and \cn{showhyphens}
-was applied to this list. The result was another list in the resulting
-\tex/ log, containing those words in a form suitable for the argument of
-\cn{hyphenation}. That list was then edited by hand to overrule
-undesirable hyphenations; words with acceptable hyphenations were
-dropped from the list, as they don't need to be repeated there.
-
-\end{document}