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Re: operator dictionary entries

From: Robert Miner <RobertM@dessci.com>
Date: Wed, 18 Jun 2003 10:29:17 -0500
Message-Id: <200306181529.h5IFTH006313@wisdom.geomtech.com>
To: gjc@inescporto.pt
CC: RobertM@dessci.com, www-math@w3.org



Hi.

> 	Thank you for the reply.
> 	Are you not confusing "stretchy" with "symmetric"?  My problem is that
> the symmetric attribute is not specified for any operator.  I realize it
> has a default value of 'true', therefore I conclude that symmetric=true
> for all operators.  Maybe this is intentional, but I find it a little
> strange that *all* operators are symmetric by default...

My apologies.  You are correct.  I was confusing stretchy with
symmetric.

However, I believe your interpretation is correct -- by default, all
operators are symmetric.  

I suppose there could be some exceptional case that I'm overlooking,
but in practice, I have only used symmetric="false" in two cases:

1) Matrix multiplication of non-square matrices:

  |a b| |A B C|   |x y|
  |c d| |D E F| = |z w|
  |e f|

  This is hard to convey as ASCII art, but what one wants to avoid is
  something like:


  |a b| |A B C|   |x y|
  |c d| |D E F| = |z w|
  |e f| |     |   |   |

2) Complicated, deeply-nested expressions that are highly unsymmetric
   around the baseline, where symmetric parentheses look odd.

There are probably more, but these are the only two cases I've
encountered.  However, both of them are clearly exceptional cases --
I'm using symmetric="false" to fix a rendering that looks odd
otherwise.  So the default is still true for all these fence
characters.  

Let me know if you can think of an operator that really shouldn't be
symmetric by default.  I would be interested to know of one!

--Robert

------------------------------------------------------------------
Dr. Robert Miner                                RobertM@dessci.com
MathML 2.0 Specification Co-editor                    651-223-2883
Design Science, Inc.   "How Science Communicates"   www.dessci.com
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Received on Wednesday, 18 June 2003 11:29:49 GMT

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