Hahn banach 2026

[mkerjean]

Motivation for this change

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]

I made a pass on the file: moving a few lemmas to mathcomp_extra.v and unstable.v, linting the code, creating a functional_analysis sub-directory, starting the changelog (NB: it contains a fix for the changelog in master which is buggy, my bad).

Since topU is defined at the top-level and therefore exposed, maybe a name like sub_initial_topology is better (btw, it should be documented).

TODO: move the new structures out of this file.

[affeldt-aist]

Compilation is fine with MathComp 2.5.0 but it looks like with a problem with the duplication of the SubNormedZmodule in MathComp and MathComp-Analysis:

Error:
You must declare the hierarchy bottom-up or add a missing join. 
There are two ways out: 
- declare structure SubNormedZmodule before structure Num.SubNormedZmodule if Num.SubNormedZmodule inherits from it; 
- declare an additional structure that inherits from both Num.SemiNormedZmodule and SubType and from which SubNormedZmodule and/or Num.SubNormedZmodule inherit.

It this is really the case, is there a trick to make it compile with both versions? @CohenCyril @gares
(It could even be a feature of HB? Again, not sure whether my diagnosis is correct...)