[comp.text.tex] Limit subscripts and nested hboxes

jeffrey@animal.cs.chalmers.se (Alan Jeffrey) (04/25/91)

Some odd behaviour running under TeX3.0...

If I create a box, containing something big (like say a 2in rule and a
letter X), but then remove it's depth and height:

   \setbox0\hbox{\vrule height 1in depth 1in X}
   \dp0=0pt
   \ht0=0pt

I can then use this as a superscript in display math mode, for example

   $\displaystyle\sin^{\usebox0}$

and I get
   
      |
      |
      X   
   sin|   } this is the height of the enclosing box
      |

as you would expect.  But if I use a mathop with \limits (for example
\sum, I get

    |     }
    |     }
    X     } this is the height of the enclosing box
    |     }
    |     }
   SUM    }

that is, {\em the height and depth of \box0 have been restored\/}!  If
I replace \usebox0 with \hbox{\usebox0} then I get what you'd expect,
that is:

    |
    |
    X
   SUM    } this is the height of the enclosing box
    |

Okay, I give in, I'm confused.  Why does TeX remove one layer of box
information when it sets the subscripts and superscripts of \mathop's
with \limits?

Cheers,

Alan.

Alan Jeffrey         Tel: +46 31 72 10 98         jeffrey@cs.chalmers.se
Department of Computer Sciences, Chalmers University, Gothenburg, Sweden