# [texhax] Cases for italic correction

Barbara Beeton bnb at ams.org
Fri Jul 20 15:48:50 CEST 2012

On Fri, 20 Jul 2012, Philip TAYLOR wrote:

Barbara Beeton wrote:

> 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.

But what of a second derivative ?  That would require d^2y/dx^2,
which will surely generate almost exactly the same inteference
as Michael asserts obtains in d^3 (but which Lars and I cannot see).

good question.  there's not a single one
in the texbook -- i checked with grep in
texbook.tex; i also checked for "d{}" and
"d\/" and several other increasingly
obscure possibilities ... nothing.

so we have no direct knuthian example.

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.
-- bb