[texhax] Cases for italic correction

[Barbara Beeton]

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