# [texhax] Cases for italic correction

Barbara Beeton bnb at ams.org
Fri Jul 20 15:05:13 CEST 2012

On Fri, 20 Jul 2012, Michael Barr wrote:

The following illustrated another use for italic correction:

\documentclass{article}

\begin{document}
$d^3=d\/^3=d{}^3$

\end{document}

I am sorry, but you have really have to see the output to appreciate the
difference.  It illustrates a real defect in tex.  The mit version of d
leans well outside the "bounding box" in a way that almost other letter
does (I think f might be another) and when you add a superscript, it
crashes into that ascender.  I wrote a book that had several hundred d^n,
where n was either a number or a letter.  These were face operators, for
which the d was the only letter ever used.  I used a macro called \dee
that added a little extra space, but an italic correction would have
worked fine.  I didn't realize until I tested it just now that a pair of
braces would also have worked.

unlike all other letters in the cm math italic
font, the d has no built-in "overhang" spacing.
i've never actually asked, but i think the
reason for this is that knuth uses d only for
indicating derivatives (as in "dx"), not for
variables, and for that use, he prefers it to
be directly adjacent to the variable involved,
not separated by a small space.

this is a frequent practice in the u.s. among
mathematicians, and ignores the iso standard
that says the derivative should be indicated
by an upright d.  (that standard was mainly
influenced by engineers and physicists,
i believe, not mathematicians; it's more
rigorously followed in europe than in the