\chapter{Introduction}
\label{introduction}
\realsections

Welcome to the \doctitle!  This document strives to be your primary
source of \latex{} symbol information: font samples, \latex{}
commands, packages, usage details, caveats---everything needed to put
tens of thousands of different symbols at your disposal.  All of the
fonts covered herein meet the following criteria:

\begin{enumerate}
  \item They are freely available from the \CTANfull
    (\url{https://www.ctan.org/}).

  \item All of their symbols have \latexE{} bindings.  That is, a user
    should be able to access a symbol by name
    (e.g.,~\cmdX{\bigtriangleup})
\end{enumerate}

\noindent
As of version~12 of the \doctitle, that second restriction has been
relaxed with the inclusion of \ref{min-latex-support}, which showcases
fonts that provide, at a minimum, either \tex\ font-metric files
(\fileext{tfm}) or the \metafont\ sources (\fileext{mf}) that produce
those font-metric files.  Some of the \ref{min-latex-support} fonts do
include \latex\ font-definition files (\fileext{fd}).  However, what
sets the fonts in \ref{min-latex-support} apart from the fonts in the
rest of the document is that they lack a \latex\ style file
(\fileext{sty}) that individually names each of the glyphs.

The restrictions listed above are not particularly limiting criteria;
the \doctitle{} contains samples of \approxcount\prevtotalsymbols{}
symbols---quite a large number.  Some of these symbols are guaranteed
to be available in every \latexE{} system; others require fonts and
packages that may not accompany a given distribution and that
therefore need to be installed.  See \TeXFAQ{installthings} for help
with installing new fonts and packages.


\section{Document Usage}

Each chapter of this document contains a number of font tables.  Each
table shows a set of symbols, with the corresponding \latex{} command
to the right of each symbol.  A table's caption indicates what package
needs to be loaded in order to access that table's symbols.  For
example, the symbols in \ref{old-style-nums}, ``\TC\ Old-Style
Numerals'', are made available by putting
``\cmd{\usepackage}\verb|{textcomp}|'' in your document's preamble.
``\AMS'' means to use the \AMS{} packages, viz.\ \pkgname{amssymb}
and/or \pkgname{amsmath}.  Notes below a table provide additional
information about some or all the symbols in that table.  Many table
notes refer to \ref{package-notes}, which discusses topics relevant to
all symbols provided by the corresponding package.

One\label{altenc} note that appears a few times in this document,
particularly in \ref{body-text-symbols}, indicates that certain
symbols do not exist in the OT1 \fntenc[OT1] (Donald\index{Knuth,
  Donald E.} Knuth's original, 7-bit \fntenc[7-bit], which is the
default \fntenc{} for \latex and \pdflatex) and that you should use
\pkgname{fontenc} to select a different encoding, such as T1 (a common
8-bit \fntenc[8-bit]\subindex{font encodings}{T1}).  That means that
you should put
``\cmd{\usepackage}\verb|[|\meta{encoding}\verb|]{fontenc}|'' in your
document's preamble, where \meta{encoding} is, e.g.,
\texttt{T1}\subindex{font encodings}{T1} or \texttt{LY1}\subindex{font
  encodings}{LY1}.  To limit the change in \fntenc[limiting scope of]
to the current group, use
``\cmd{\fontencoding}\verb|{|\meta{encoding}\verb|}|\cmd{\selectfont}''.
Note that this guidance applies only to \latex and \pdflatex;
\lualatex and \xelatex default to the TU (``\tex
Unicode'')\index{Unicode} \fntenc[TU], which directly supports
Unicode\index{Unicode} character entry.

\ref{addl-info} contains some additional information about the symbols
in this document.  It warns that symbol names are not unique across
packages; discusses scaling of mathematical symbols; provides
additional, per-package usage information; gives examples of how to
create new symbols out of existing symbols; explains how symbols are
spaced in math mode; compares various schemes for boldfacing symbols;
presents \latex{} \ascii and Latin~1\index{Latin 1} tables; describes
how to input and output Unicode\index{Unicode} characters; and
provides some information about this document itself.  The \doctitle{}
ends with an index that facilitates searching.

A companion document, \rawtables, also presents a large number of
symbols but with a very different structure from this document.
\rawtables\ includes only symbols produced via a font file, while this
document also includes composite symbols (combinations of two or more
glyphs) and symbols drawn as pictures (using, e.g., \TikZ)\@.  This
document sorts symbols by category while \rawtables\ sorts symbols by
underlying font file.  The two documents are intended to complement
each other.  It is usually easier to find a desired symbol in The
Comprehensive \latex\ Symbol List, but \rawtables\ is helpful for
identifying related symbols, for finding symbols that exist in some
font but are not exposed to the user via a \latex\ package (or that
this document inadvertently overlooked), and for the font name and
character position needed to typeset a single symbol in isolation.
The last of those is especially important for math symbols.
\tex\ imposes a limitation of at most 16 math alphabets per document,
but symbols typeset with \cmd{\font} and \cmd{\char} are text symbols
and do not consume a math alphabet.  They are less convenient to use
within a mathematical expression, however.

\ifcomplete

\section{Frequently Requested Symbols}

There are a number of symbols that are requested over and over again
on \ctt.  If you're looking for such a symbol the following list will
help you find it quickly.

\newenvironment{symbolfaq}{%
  \setlength{\columnsep}{3em}%
  \begin{multicols}{2}%
  \setlength{\parskip}{1ex}%
  \newcommand{\faq}[2]{%
    \noindent##1\quad\dotfill\quad\makebox[1em][r]{##2}\par}%
}{%
  \end{multicols}%
}

\begin{symbolfaq}
  \faq{\textvisiblespace, as in
       ``Spaces\textvisiblespace are\textvisiblespace significant.''}
      {\pageref{text-predef}}
  \faq{\~{\i}, \H{\i}, \u{\i}, \v{\i}, etc.\ (versus
       \encOone{\~i, \H{i}, \u{i}, and \v{i}})}
      {\pageref{text-accents}}
  \faq{\textcent}
      {\pageref{tc-currency}}
  \faq{\EUR}
      {\pageref{marv-currency}}
  \faq{\textcopyright, \textregistered, and \texttrademark}
      {\pageref{tc-legal}}
  \faq{\textperthousand}
      {\pageref{tc-misc}}
  \faq{$\oiint$}
      {\pageref{txpx-large}}
  \faq{$\therefore$}
      {\pageref{ams-rel}}
  \faq{$\coloneqq$ and $\Coloneqq$}
      {\pageref{txpx-rel}}
  \faq{$\lesssim$ and $\gtrsim$}
      {\pageref{ams-inequal-rel}}
  \faq{$\MDOTSiddots$}
      {\pageref{mathdots-dots}}
  \faq{\textdegree, as in ``180\textdegree'' or ``15\textcelsius''}
      {\pageref{tc-math}}
  \faq{\mathscr{L}, \mathscr{F}, etc.}
      {\pageref{alphabets}}
  \faq{\mathbbm{N}, \mathbbm{Z}, \mathbbm{R}, etc.}
      {\pageref{alphabets}}
  \faq{{\Large\textcalligra{r}}}
      {\pageref{alphabets}}
  \faq{$\dashint$}
      {\pageref{dashint}}
  \faq{\diatop[{\diatop[\'|\=]}|a],
       \diatop[{\diatop[\`|\^]}|e], etc.
       (i.e., several accents per character)}
      {\pageref{multiple-accents}}
  \faq{$<$, $>$, and $|$ (instead of \encOone{<, >, and |})}
      {\pageref{upside-down}}
  \faq{\textasciicircum\ and \textasciitilde\ (or $\sim$)}
      {\pageref{page:tildes}}
\end{symbolfaq}

\fi    % ifcomplete
