# Re: Too narrowly defined: DIVISION SIGN & COLON

From: Hans Aberg <haberg-1_at_telia.com>
Date: Thu, 12 Jul 2012 22:02:26 +0200

On 12 Jul 2012, at 21:03, Jukka K. Korpela wrote:

> 2012-07-12 21:07, Asmus Freytag wrote:
>
>> What the examples show from TeX is that colon and ratio cannot be
>> substituted for each other without affecting the display.
>
> This looks like a problem in TeX rather than character standards. If TeX can space $a+b$ properly, what’s the issue with $a:b$? And when I tested it, I got proper spacing, corresponding to the example in “Detailtypographie” (which mentions that the colon, Doppelpunkt, is used “eventuell aus didaktischen Gründen, sonst eher veraltet oder als »verhält sic zu« verwendet”).
>
> However, it might be argued that disambiguation is desirable, because COLON is also used as punctuation symbol in mathematical expressions, as in “f: A → B” and here (arguably) there should be some spacing after the colon but not before it.

In original TeX, there should be $a:b$ and $f\colon A \rightarrow B$. If you want to use Unicode characters, it is possible with (compiled with lualatex):
\documentclass{article}
\usepackage{amsmath}

\usepackage{fontspec}
\usepackage[math-style=literal,colon=literal]{unicode-math}

\defaultfontfeatures{Ligatures=TeX}

\setmainfont{XITS}
\setmathfont{XITS Math}

\begin{document}
$f: A → 𝑩, 𝐁, B, 𝗕, 𝘽$ and $a∶b$.
\end{document}

Here, colon=literal causes the two colon types behave as marked in Unicode, and math-style=literal causes the same for the mathematical semantic styles.

Hans
Received on Thu Jul 12 2012 - 15:03:42 CDT

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