Hi Ikumi, many thanks for your feedback.

> Is it really necessary to delete leading whitespaces? At the end of this
> function, we do `indent-region', which I expect would do the job. (And
> then, we can just call `delete-trailing-whitespace'.)

Deleting whitespace is relevant when converting from display to inline.
It seemed like the appropriate way to handle the variety of ways users
might write display math, e.g., $$ x + y $$ with or without newlines.
Other suggestions would be welcome.

I've incorporated all the other suggested changes, together with the
following further changes:

- replaced calls to LaTeX-environment-list-filtered with a new helper
  function LaTeX-math-environment-list (which could be made internal, I
  suppose?) that returns a more suitable list.

- factored our a helper function LaTeX--strip-labels.

Any further feedback welcome.

Thanks, best,

Paul