Re: DeclareMathOperator and digit in operator name

With default catcodes TeX command names may not contain digits.
the previous behaviour accidentally caused the command `\Fast` to be
defined and no error message is given.

Due to unrelated changes the erroneous behaviour is now caught earlier and
you get an error at the point of definition.

In either case the behaviour is undefined accidental action of how the
unexpected tokens `2Sum` fall through.

David




On Wed, 17 Dec 2025 at 14:33, Vincent Lefevre <[email protected]> wrote:

> Hi,
>
> After a recent upgrade of TeX Live in Debian/unstable
> (2025.20251127 snapshot?), the following LaTeX file fails
> to compile:
>
> \documentclass{article}
> \usepackage{amsopn}
> \DeclareMathOperator{\Fast2Sum}{Fast2Sum}
> \begin{document}
> $\Fast2Sum(X)$
> \end{document}
>
> with an error on the \DeclareMathOperator.
>
> This is due to the "2" in the operator name \Fast2Sum.
>
> However, in
>
>
> https://mirrors.ctan.org/install/macros/latex/required/latex-amsmath.tds.zip
>
> I cannot see any corresponding change mentioned in "changes.txt".
>
> So I'm wondering where this has changed in TeX Live and whether
> this is a change done on purpose. In the latter case, where is
> this change documented?
>
> --
> Vincent Lefèvre <[email protected]> - Web: <https://www.vinc17.net/>
> 100% accessible validated (X)HTML - Blog: <https://www.vinc17.net/blog/>
> Work: CR INRIA - computer arithmetic / Pascaline project (LIP, ENS-Lyon)
>