Re: Math literal colon

From: Hans Aberg <haberg-1@telia.com>
To: mailing list for ConTeXt users <ntg-context@ntg.nl>
Subject: Re: Math literal colon
Date: Mon, 20 Jul 2015 19:08:46 +0200	[thread overview]
Message-ID: <C5C3247D-3298-4E8B-B32B-6ED0453F15D8@telia.com> (raw)
In-Reply-To: <alpine.OSX.2.02.1507201227300.12932@nqv-znpobbx>

> On 20 Jul 2015, at 18:37, Aditya Mahajan <adityam@umich.edu> wrote:
> 
> On Mon, 20 Jul 2015, Hans Aberg wrote:
> 
>> 
>>> On 20 Jul 2015, at 16:40, Aditya Mahajan <adityam@umich.edu> wrote:
>>> On Mon, 20 Jul 2015, Hans Aberg wrote:
>>>> The LaTeX package unicode-math has an option colon=literal, which makes it behave as in math functions (as in example below). Has ConTeXt a similar option?
>>> No. You have to use \colon.
>> 
>> It would be nice with such an option, as it helps the readability of the input files.
> 
> There are two uses of colon in math, as a relation (in sets \{ x : f(x) = 0 \} and in ratios A:B, etc) and as a punctuation ($f \colon A -> B, etc.[1]). Only one of them can be mapped to the literal :, the other must use a macro name. Knuth chose to map : to the relation and mapped \colon to a punctuation and every other macro package follows that convention.

Right. Perhaps he didn’t use functions much. :-)

> It is easy to change the mapping, but if the mapping is reversed, is there is standard name for : as a relation?

It seems that “\:” might be used. I get an error when trying to use it in luatex. But note:

In pure math, “:” is also used for projective coordinates, it does not seem to have operator spaces around them. This is what I think is the right look:
  https://en.wikipedia.org/wiki/Homogeneous_coordinates#Notation

There is also Unicode ∶ RATIO U+2236.

So a proposal might be to keep \colon, and make a new \ratio for those that want to use the operator : in ASCII. The : without spaces might perhaps be called \proj or something.

Looking at
  https://en.wikipedia.org/wiki/Mathematical_Operators
a UTF-8 mapping would be sending U+2236 to \ratio, the operator :. There is no special colon for the other uses, function and projective coordinates, it seems.

So the \: might be mapped to \proj or \ratio according to taste.

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