[texhax] Something funny about \mathop (fwd)

Lars Madsen daleif at imf.au.dk
Mon Jul 26 15:13:55 CEST 2010

Michael Barr wrote:
> I have answered my own question below.  The answer is found in point 13 
> of Appendix G of The TeXBook bottom of page 443 and top of 444 in my 
> (the first) edition.  Although I didn't follow the technical details it 
> is clear that TeX will lower a single character \mathop to center it 
> along the horizontal axis.  It is not clear why an empty pair of braces 
> defeats this mechanism but it does.  It is clear that this was intended 
> for things like integral signs and not single alphabetic characters, but 
> it doesn't distinguish between them.  Curiously, this is not indexed 
> (not under \mathop, in any case) in the TeXBook.
> Michael Barr

Thanks for the reference.

TeX deals in atoms, and since {} is the empty atom {}I and I{} are two 
atoms, so it falls in the second category



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