[texhax] Cases for italic correction

[Heiko Oberdiek]

On Fri, Jul 20, 2012 at 09:48:50AM -0400, Barbara Beeton wrote:

> however, i don't see the difference either;
> here's my test:
> 
>   \documentclass[12pt]{article}
>   \begin{document}
>   \Large
>   $dx + d^2x + d{}^2x + d\/^2x$
>   \end{document}
> 
> definitely a puzzlement.

>From "The TeXbook", "Appendix G: Generating Boxes from Formulas":
| Chapter 17 stated that the most important components of math
| lists are called atoms, and that each atom has three fields
| called its nucleus, subscript, and superscript. We frequently need
| to execute a subroutine called "Set box x to the so-and-so field
| in style such-and-such." This means (a) if the specified field is
| empty, x is set equal to a null box; (b) if the field contains
| a symbol, x is set to an hbox containing that symbol in the
| appropriate size, and the italic for the character is included
| in the width of the box; [...]

The following example shows the automatic insertion of the
italic correction for the "f" (\kern2.65642):

\documentclass[12pt]{article}

\showboxdepth=\maxdimen  
\showboxbreadth=\maxdimen
\tracingonline=1

\begin{document}
\Huge

$f^3=f\/^3=f{}^3$
\showlists

\end{document}

The italic correction is also inserted (\kern0.0), but it is
zero, because the preceding character is already corrected:

| \OML/cmm/m/it/24.88 f
| \kern2.65642
| \kern0.0
| \hbox(13.36923+0.0)x10.01173, shifted -9.02875
| .\OT1/cmr/m/n/20.74 3

Yours sincerely
  Heiko Oberdiek