[texhax] Weird behavior of \mathop

[Michael Barr]

Thanks to Donald Arsenau for actually explaining this.  But on the basis 
of what he said, I would expect
  \def\E{\mathop{\bf {E}}}
to work.  However,
  \def\E{\mathop{\bf E\kern0pt}}
works perfectly.

If you actually want this (somewhere I read a rather unconvincing 
explanation why Knuth did), then \setbox0=\hbox{$\E$} ought to get around 
the bug.

Michael