[latexrefman] Add Arrows subsection

[Karl Berry]

    Karl, what do we do about arrows such as \leadsto, which are not in
    standard LaTeX so the .pdf gives an error? 

There is no magic bullet (or arrow :). We will have to define them. Since
\leadsto (et al.) are just characters in the lasy fonts, it should be
easy enough to do. There are only about a dozen defined in latexsym.dtx.
(If I were still maintaining Texinfo, I would define them there, but I
wouldn't go that route now.)

I can work on this if you like, although if one of you wants to make the
plain TeX definitions to access them, so much the better. And/or, if
anyone could look up the Unicode code points (which I presume we'd want
for the HTML output), that would be great.

\DeclareMathSymbol\mho     {\mathord}{lasy}{"30}
\DeclareMathSymbol\Join    {\mathrel}{lasy}{"31}
\DeclareMathSymbol\Box     {\mathord}{lasy}{"32}
\DeclareMathSymbol\Diamond {\mathord}{lasy}{"33}
\DeclareMathSymbol\leadsto {\mathrel}{lasy}{"3B}
\DeclareMathSymbol\sqsubset{\mathrel}{lasy}{"3C}
\DeclareMathSymbol\sqsupset{\mathrel}{lasy}{"3D}
\DeclareMathSymbol\lhd     {\mathbin}{lasy}{"01}
\DeclareMathSymbol\unlhd   {\mathbin}{lasy}{"02}
\DeclareMathSymbol\rhd     {\mathbin}{lasy}{"03}
\DeclareMathSymbol\unrhd   {\mathbin}{lasy}{"04}

    I thought about putting
    in the AMS arrows, because they are pretty standard, but then I'd
    get two dozen errors.

They are AMS, not core LaTeX, and require \usepackage{amswhatever},
right? Same reasoning as usual; I wouldn't include them (now). The ams*
packages would surely be the first ones to add after core LaTeX is done,
but ... --thanks, karl.