derive_mx

[affeldt-aist]

Motivation for this change

two lemmas from robot-rocq that are also useful for ode @CohenCyril

Checklist

• added corresponding entries in CHANGELOG_UNRELEASED.md

• added corresponding documentation in the headers

Reference: How to document

Merge policy

As a rule of thumb:

• PRs with several commits that make sense individually and that
  all compile are preferentially merged into master.
• PRs with disorganized commits are very likely to be squash-rebased.

Reminder to reviewers

• Read this Checklist
• Put a milestone if possible
• Check labels

[affeldt-aist]

@holgerthies @yosakaon @IshiguroYoshihiro if one of you has a minute, could you take a quick look?

Since theses lemmas have already by tested by others and proved useful elsewhere, I think that it is reasonable to merge them if CI is green and if there are no objections.

[CohenCyril]

There probably also are instances of is_diff and is_derive to add, but one should make sure they are not looping.

[affeldt-aist]

There probably also are instances of is_diff and is_derive to add, but one should make sure they are not looping.

Indeed, I also thought (but was quick to forget) that we do not honor the intended API that ought to provide automation. I started mimicking what was done for other constructions but I am starting being confused. Can you take a quick look at affeldt-aist@30c013a and open my eyes?