# Re: Too narrowly defined: DIVISION SIGN & COLON

From: Hans Aberg <haberg-1_at_telia.com>
Date: Wed, 11 Jul 2012 16:20:26 +0200

On 11 Jul 2012, at 15:59, Khaled Hosny wrote:

> On Wed, Jul 11, 2012 at 10:47:33AM +0200, Hans Aberg wrote:
>> On 11 Jul 2012, at 03:51, Khaled Hosny wrote:
>>
>>> It can be handled at a different level; when one types 3:5 in a
>>> Unicode-complient TeX engine, what gets output to the output file is the
>>> ratio not the colon, and colon gets output with 3\colon{}5.
>>
>> Actually, TeX does it wrongly relative Unicode: a colon ":" in the
>> input file should expand TeX $\colon$, whereas "∶" RATIO U+2236 should
>> expand to TeX $:$.
>
> It is a kind of primitive input method, like using / for division slash
> and * for asterisk operator, and ratio is more frequent in math than the
> colon. (original TeX handled this by having different glyphs/glyph
> classes in math than TeX, Unicode-compliant TeX engines map them to the
> appropriate Unicode character).

There are a number of other incompatibilities between original TeX and Unicode:

For example, ASCII letters are in TeX math mode typeset in italics, but Unicode has a mathematical italics style, so ASCII letters should be typeset upright in a strict Unicode mode. And similar for Greek letters, I gather.

If I try the code below in lualatex, then the 𝑩 and the 𝐁 both come out typeset upright.

Also, in the code there is an example where spacing produces a semantic difference: {A: B} is the set of all A satisfying the predicate B, whereas {A : B} is the set of the single element A : B. (It is more common to use "|" nowadays in the first case, but it is also used as an operator.)

Hans

----
\documentclass{article}
\usepackage{amsmath}
\usepackage{fontspec}
\usepackage{unicode-math}
\defaultfontfeatures{Ligatures=TeX}
\setmainfont{XITS}
\setmathfont{XITS Math}
\begin{document}
$f\colon A → 𝑩, 𝐁$ and $x = c:d:e$
$f∶ A → B$ and $x = c:d∶e$
$\{A\colon P\}$ and $\{A:P\}$.
\end{document}
----

Received on Wed Jul 11 2012 - 09:24:21 CDT

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