# RE: Stretchy equal sign for commutative diagrams

From: Daniel Marques <dani@wiris.com>
Date: Mon, 25 Mar 2013 10:10:25 +0100
To: David Carlisle <davidc@nag.co.uk>, www-math@w3.org
I agree with David that using the equal sign has some implications. For
example, the distance of the two horizontal lines might not be the desired
one. Using the stretchy part of the double arrow or the box drawing have
the extra advantage that the parallel vertical bars (and maybe diagonal)
are also available and consistently drawn.

Dani from WIRIS

-----Original Message-----
From: David Carlisle [mailto:davidc@nag.co.uk]
Sent: sábado, 23 de marzo de 2013 17:57
To: www-math@w3.org
Subject: Re: Stretchy equal sign for commutative diagrams

On 23/03/2013 15:02, Frédéric WANG wrote:
> Hi all,
>
> We are implementing the AMScd extension in MathJax:
>
> https://github.com/mathjax/MathJax/issues/420
>
> and one horizontal stretchy operator that is needed is the character
> for two parallel horizontal bars. We use the equal sign "=" and it
> seems that LaTeXML does the same.
>
> I'm wondering if others have considered this operator and whether they
> used a different Unicode code point for that. The equal sign is not
> stretchy by default (that makes sense) and I don't see constructions
> in the Open Type Math table of e.g. the STIX fonts.
> This is not available in Gecko either. That's probably not hard to
> implement (one could repeat the equal sign or use the middle glyphs
> available for the "Double Right Arrow"), but I just want to coordinate
> with other projects and keep things consistent.
>

I suppose U+2550 (from the box drawing block) is another possibility but
using an equals or an arrow part is more likely to blend in with other
arrows used I'd guess. AMScd itself I think doesn't use a font glyph at
all for this but uses a rule (I'm not sure that's relevant here though, I
think you'd want a character and stretchy attribute for MathML.

David

Received on Monday, 25 March 2013 09:10:56 UTC

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