question about \DeclareMathActive and unbraced super/subscript

Question

I find the asterisk of kpfonts too small when used in super/subscripts so, following answers here and here, I'm using @egreg's brilliant \DeclareMathActive to redefine * in math mode as \textstyle\ast:

\documentclass{article}
\usepackage{kpfonts,etoolbox}
\makeatletter
\newcommand{\DeclareMathActive}[2]{%
  % #1 is the character, #2 is the definition
  \expandafter\edef\csname keep@#1@code\endcsname{\mathchar\the\mathcode#1 } \begingroup\lccode~=#1\relax \lowercase{\endgroup\def~}{#2}% \AtBeginDocument{\mathcode#1="8000 }%
}
\newcommand{\std}[1]{\csname keep@#1@code\endcsname}
\patchcmd{\newmcodes@}{\mathcode\-\relax}{\std@minuscode\relax}{}{\ddt} \AtBeginDocument{\edef\std@minuscode{\the\mathcode-}}
\makeatother
\DeclareMathActive{*}{{\textstyle\ast}}
\begin{document}
$f_\mathscr{F} \quad f^\mathscr{F} \quad R^*$
$A*B$
\end{document}

This works wonderfully, except that in order to make R^* work without bracing the * (as in R^{*}), I have to add braces around \textstyle\ast. This then removes the \mathbin spacing in expressions like A*B.

Is there any hack to \DeclareMathActive that would allow for both unbraced * in super/subscripts and correct spacing in A*B? One idea is to extend DeclareMathActive to take arguments like \mathchoice:

\DeclareMathActiveChoice{<char>}{<display code>}{<text code>}{<script code>}{<scriptscript code>}

Then one could use \DeclareMathActiveChoice{*}{\ast}{\ast}{{\textstyle\ast}}{\ast}.

However I have no idea how to implement such an extension.

Just for context, here's why I want to do this at all. Compare

And for a professionally typeset comparison, here's the same line in Hartshorne's Algebraic Geometry:

you could make ^ math active defined by \def^#1{\sp{#1}} — David Carlisle, Apr 29 '23 at 18:58
Thanks, \catcode`\^=\active \def^#1{\sp{#1}} works. One also has to do \catcode`\_=\active \def_#1{\sb{#1}}. I thought perhaps this would break e{_}-type args of \NewDocumentCommand but it seems to work fine. Is there any downside? Also feel free to post your comment as an answer — mbert, Apr 29 '23 at 19:27
@DavidCarlisle It seems this breaks \input{my_file}, which I suppose is expected — mbert, Apr 29 '23 at 19:37
not if you make it math active, that's the point, it only affects math mode — David Carlisle, Apr 29 '23 at 19:46
@DavidCarlisle Do you mean with something like \ifmmode, with \DeclareMathActive, or another way? — mbert, Apr 29 '23 at 20:05
you don't need ifmmode, use mathcode "8000 or, since you have defined it \DeclareMathActive something like \def\foohat#1{\sp{#1}}\DeclareMathActive{^}{\foohat} I guess — David Carlisle, Apr 29 '23 at 20:13
@DavidCarlisle I must be missing something because that gives me the bracing error, Missing { inserted — mbert, Apr 30 '23 at 00:09
Looks like duplicate of math mode - How to avoid using curly braces when placing a \DeclareMathOperator command in subscript or superscript, while preserving spacing? - TeX - LaTeX Stack Exchange ? — user202729, Apr 30 '23 at 14:52
This is one of the reasons why I prefer using macros for everything instead of manual syntax like ^*. — Gaussler, Sep 25 '23 at 16:15

David Carlisle · Accepted Answer · 2023-04-30T08:42:05.033

1

You could make ^ and _ grab arguments like a macro, which would mean x^\frac{1}{2} would no longer work, it would need x^{\frac{1}{2}} but that is no great loss.

\documentclass{article}
\usepackage{kpfonts,etoolbox}
\makeatletter
\newcommand{\DeclareMathActive}[2]{%
  % #1 is the character, #2 is the definition
  \expandafter\edef\csname keep@#1@code\endcsname{\mathchar\the\mathcode#1 } \begingroup\lccode~=#1\relax \lowercase{\endgroup\def~}{#2}% \AtBeginDocument{\mathcode#1="8000 }%
}
\newcommand{\std}[1]{\csname keep@#1@code\endcsname}
\patchcmd{\newmcodes@}{\mathcode\-\relax}{\std@minuscode\relax}{}{\ddt} \AtBeginDocument{\edef\std@minuscode{\the\mathcode-}}
@makeother^
@makeother_
\makeatother
\DeclareMathActive{*}{\mathbin{\textstyle\ast}}
\DeclareMathActive{^}{\foosup}
\DeclareMathActive{_}{\foosub}
\def\foosup#1{\sp{#1}}
\def\foosub#1{\sb{#1}}
\begin{document}
$f_\mathscr{F} \quad f^\mathscr{F} \quad R^*$
$A*B$
\end{document}

edited Apr 30 '23 at 08:42

answered Apr 30 '23 at 00:20

David Carlisle

757,742

There is a special place in Hell for people who type x^\frac{1}{2}. – Gaussler Apr 30 '23 at 07:20
@Gaussler they can claim redemption by using x^\frac12 – David Carlisle Apr 30 '23 at 08:41
For those, there is an even more special place, much deeper down in Hell. – Gaussler Apr 30 '23 at 10:39
@DavidCarlisle Thank you this is great. Why do auxiliary commands \foosup have to be defined? \DeclareMathActive{^}{\sp} does not work but I don't know why – mbert Apr 30 '23 at 16:38
1

@mbert \DeclareMathActive{^}{\sp} would do nothing as \sp is ^ you need a macro taking #1 that is the point of the definition – David Carlisle Apr 30 '23 at 16:44
I see, I misunderstood \sp – mbert Apr 30 '23 at 16:56

question about \DeclareMathActive and unbraced super/subscript

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