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Re: LeftRightArrow equivalence operator?




Hi Hugh,

> The MathML rec includes a RightArrow, implies content element, but
> apparently absent is a LeftRightArrow, equivalence operator. Unless I'm
> missing something?

I think you're missing something.  I assume you are using TeX
terminology here, and are thinking of a double arrow with heads at
both ends typically indicating the (logicial) equivalence "if and only
if".

The official unicode point for that character is 0x21D4 and its
official unicode entity name is ⇔.  In MathML it also has a
a couple of aliases which are valid -- ⇔ and
⇔.

For some reason that I don't know, the TeX name lost out here, and the
obvious guess -- ↔ -- is actually a synonym for TeX's
\leftrightarrow.  

In general, most of these naming issues came up as uncomfortable
compromises.  MathML has *lots* more characters (and specifically
arrows) than TeX and though in general we tried very hard to stay
compatible with TeX names, that wasn't always possible, especially
since TeX, LaTeX, AMSTeX etc are not always consistent amongst
themselves.

--Robert

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Robert Miner                          http://www.webeq.com
Geometry Technologies, Inc.           email: rminer@geomtech.com
                                      phone: 651-223-2884
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