# Fwd: Re: [texhax] Correcting for math-mode kerning before commas and periods?

Uwe Lück uwe.lueck at web.de
Thu Oct 20 13:54:37 CEST 2005

```At 18:06 16.10.05, Alexander McCormmach wrote:
>Uwe Lück wrote:
><snip/>
> > OK, TeX first builds a math list from the "input stream"
> > according to Chapters 24 and 26. When some \kern<wd>
> > comes in, a kern of width <wd> is appended to the math list.
> > When an \unkern follows immediately, that kern of width
> > <wd> is removed again. When an \unkern comes in that
> > has not been preceded by a \kern<wd> immediately, it is
> > just ignored. Thus a math list can contain kerns, but not
> > \unkern's. However, the kern (which is a kern indeed!)
> > from the automatic italic correction according to
> > Appendix G Rules 13, 17, 18f can come in only when the
> > math list has been finished and is converted into a
> > horizontal list, and there is no way for an \unkern to
> > interfere here. Even \$\unkern can't, because it is screened
> > off by the final \mathoff.
>
>Yes, this seems to be what is going on, and now I am at the point of
>trying to find a practical solution. From my cross-post on comp.text.tex
>[1], it was suggested that inserting a final subscript would prevent the
>extra kerning, as follows:
>
>   \newcommand\nok{_{\kern-\scriptspace}}
>   Let \$U\$ be the union of sets \$R\$ and \$S\nok\$.
>
>which works well for Computer Modern fonts. But just to add a little
>spice to the mix, it seems this solution doesn't work for my preferred
>font, the venerable Times Roman, via the txfonts package. It turns out
>that txfonts has TeX putting some kind of space *in between* math-mode
>letters and their subscripts. I used the following test input both as-is