# Re: Too narrowly defined: DIVISION SIGN & COLON

From: Khaled Hosny <khaledhosny_at_eglug.org>
Date: Wed, 11 Jul 2012 16:33:49 +0200

On Wed, Jul 11, 2012 at 04:20:26PM +0200, Hans Aberg wrote:
> 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.

There is a “literal” mode in unicode-math package just for that, check
its manual for more details.

> 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.)

There is also an option to control colon vs. ratio behaviour, but this
is getting off-topic IMO.

Regards,
Khaled
Received on Wed Jul 11 2012 - 09:35:54 CDT

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