Interchange `\colon` and `:`

Question

I know that there is a typographical difference between using : and \colon in math mode, because : is considered to be a relation. However, I use \colon far more often than :, so I would like to interchange both. Is that possible?

Phelype Oleinik · Accepted Answer · 2019-09-22T13:48:19.503

6

\colon and : are defined in fontmath.ltx using:

\DeclareMathSymbol{\colon}{\mathpunct}{operators}{"3A}
\DeclareMathSymbol{:}{\mathrel}{operators}{"3A}

which makes \colon a punctuation and : a relation symbol, as you said yourself.

You can swap the definitions:

\DeclareMathSymbol{:}{\mathpunct}{operators}{"3A}
\DeclareMathSymbol{\colon}{\mathrel}{operators}{"3A}

As egreg noted, amsmath has a different definition of \colon, which does not rely on TeX's primitive math spacing. To swap the definitions of : and \colon with amsmath you need to make : a math-active character (I did that using egreg's \DeclareMathActive) and un-define \colon prior to using \DeclareMathSymbol:

\usepackage{amsmath}
% From https://tex.stackexchange.com/a/299805/134574
\newcommand{\DeclareMathActive}[2]{%
  \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}
% amsmath's definition of \colon:
\DeclareMathActive{:}{\nobreak\mskip2mu\mathpunct{}\nonscript
  \mkern-\thinmuskip{\std{:}}\mskip6muplus1mu\relax}
% undefine then redefine \colon:
\let\colon\UndefineD
\DeclareMathSymbol{\colon}{\mathrel}{operators}{"3A}

edited Sep 22 '19 at 13:48

answered Sep 22 '19 at 13:06

Phelype Oleinik

70,814

With that I get: LaTeX Error: Command \\colon' already defined.The command for:` works though. Is there any way to "remove" commands? – red_trumpet Sep 22 '19 at 13:18
1

put \let\colon\relax before the definition @red_trumpet – David Carlisle Sep 22 '19 at 13:20
1

@red_trumpet \let\colon\relax or \let\colon\undefined. Related question – schtandard Sep 22 '19 at 13:21
Thanks now it works! What's the difference between relax and undefined? – red_trumpet Sep 22 '19 at 13:27
@red_trumpet What they said :-) \relax is a "do-nothing", so usually if a command is equal to \relax it is "free to be redefined". \undefined is an undefined command. \SomethingImPrettySureIsNotDefined would've worked too. The error only appears if \colon is defined to be something else though... – Phelype Oleinik Sep 22 '19 at 13:30
Okay, so using an undefined command results in an error (command not found), and using a \relaxed command just does nothing. Thanks! – red_trumpet Sep 22 '19 at 13:32
I'd like to recall that \colon has a different definition in amsmath. – egreg Sep 22 '19 at 13:36
@egreg Nice recalling. That explains the error. Thanks :-) – Phelype Oleinik Sep 22 '19 at 13:48
@red_trumpet See the edit. – Phelype Oleinik Sep 22 '19 at 13:49
@PhelypeOleinik I’m gonna define \UndefineD in my preamble and sue you when the code fails. ;-) – Gaussler Aug 16 '22 at 10:28

Interchange `\colon` and `:`

1 Answers1