integrable and norm

[affeldt-aist]

Motivation for this change

missing lemme about integrable and norm

@holgerthies @IshiguroYoshihiro

Checklist

• [x] 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