# [OS X TeX] Strange error

Alain Schremmer schremmer.alain at gmail.com
Fri Nov 16 13:15:05 EST 2007

On Nov 12, 2007, at 5:54 PM, Morten Høgholm wrote:

> On Mon, 12 Nov 2007 23:41:30 +0100, Ross Moore wrote:
>
> Hello Ross,
>
>> What I don't understand is the subtle difference that using
>>   \begingroup ... \endgroup  makes in this context.
>> How is it different to  { ... } ?   or  \bgroup ... \egroup  ?
>>
>> Most curious.
>
> And rightly so! :-)  For some reason, DEK decided to implement
> {...} to act as a shorthand for \mathord{...} in math mode. And so
> nice TeX programmers like Didier Verna get cought by it sometimes
> when all they want is grouping but they wind up with more than they
> wished for. \bgroup and \egroup act as { and } in this case and
> produce an Ord.
>
> Somewhat related are the well-known (for those who know too much!)
>   \iffalse {\fi \iffalse`}=0 \fi
>   \iffalse`{=0 }\fi
> when it comes to opening special groups in alignments without
> accidentally introducing extra math atoms.

Well, as usual, I am completely impressed. I mean, I have no idea
what this exchange with Moore is about but less than an hour after I
started getting /really/ worried, first I got Moore's fix, then
Hoegholm, and finally Verna.

Grateful regards to all
--schremmer