Eli Zaretskii <eliz@gnu.org> writes:

[...]

>> 'plusp' is a classic Common Lisp predicate (that also seems to be
>> defined in Emacs).  It is equivalent to (> x 0)… maybe you prefer that.
>> Should I fix my patch?
>
> Where is it defined?  It isn't defined in "emacs -Q", and not after
> loading image-dired.  (Tested in Emacs 29.)

C-h f gives me this:
--8<---------------cut here---------------start------------->8---
plusp is an alias for ‘cl-plusp’ in ‘cl.el’.

This function is obsolete since 27.1; use ‘cl-plusp’ instead.
--8<---------------cut here---------------end--------------->8---

… anyway here is an updated version of the patch to avoid this.