Wrong spacing with math mode inside sl in plain TeX

Question

Here is a minimal example of a problem I encounter sometimes:

{\sl Let $\cal U$ be}
\bye

In the output U is much closer to "Let" than to "be". Is there an equivalent to the italic correction to be applied?

Answer 1

TeX automatically adds the italic correction after a math character, in this situation.

In select cases, you can remove this italic correction:

\def\nocorr{_{\kern-\scriptspace}}

Let $\cal U$ be

Let $\cal U\nocorr$ be

{\sl Let $\cal U$ be}

{\sl Let/ $\cal U$ be}

{\sl Let/ $\cal U\nocorr$ be}


\bye

The trick is that the italic correction is not inserted if there is a subscript but no superscript; however one has also to remove the \scriptspace.

Note the slight differece between lines 3 and 4.