[texhax] Correcting for math-mode kerning before commas and periods?

Uwe Lück uwe.lueck at web.de
Sun Oct 16 13:00:16 CEST 2005

At 21:27 15.10.05, Oleg Katsitadze wrote:
>On Sat, Oct 15, 2005 at 07:57:09PM +0200, Uwe L?ck wrote:
> > According to TeXbook p. 280f., there is a primitive command \unkern,
> > such that \unkern$ should serve your desire -- since the italic correction
> > is a kern (TeXbook p. 287).
>\unkern does not seem to work here.

Indeed, I apologize. In horizontal mode, the italic correction can be 
and measured through \lastkern, but not in math mode. With \showlists
you see that the italic correction appears as a \kern, but this seems to be
a lie, somewhat. \lastkern is 0pt. Indeed, TeXbook p. 441 rather tells that
the width of the box that a character forms includes the italic correction of
that character. This indicates that after forming the box, its \wd is 
by the dimension that \/ would use for its \kern (instead of executing that

Now I have devised a macro \unkerned which seems to work at least with
characters (not with symbols etc.) -- see below. In order to avoid the
automatic pseudo-kerning, it measures the difference of the character
with vs. without the italic correction by using the _math_ font in
_non-math_ mode. (LaTeX is used for this implementation of the
algorithm.) In a first line, the macro is used; a second line shows that
the macro really makes a visible difference. The \showlists for the first
line shows \kern'ing values that add up to 0pt indeed.

Uwe L.


   \edef\that at font{\the\textfont\@ne}%
   \settowidth\dimen@{\that at font#1}%
   \settowidth\dimen@{\that at font#1\/}%

\showboxbreadth=20 \showboxdepth=0
% \itshape f\/\showthe\lastkern

\end{document} %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

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