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@mans0954 mans0954 commented Jun 24, 2025

The bipolar theorem states that the polar of the polar of a set s is equal to the closed absolutely convex hull of s.

The argument here follows Conway, Chapter V. 1.8.

This PR continues the work from #20843.

Original PR: #20843

mans0954 and others added 10 commits September 30, 2025 17:46
Co-authored-by: Filippo A. E. Nuccio <filippo.nuccio@univ-st-etienne.fr>
Co-authored-by: Filippo A. E. Nuccio <filippo.nuccio@univ-st-etienne.fr>
Co-authored-by: Filippo A. E. Nuccio <filippo.nuccio@univ-st-etienne.fr>
Co-authored-by: Filippo A. E. Nuccio <filippo.nuccio@univ-st-etienne.fr>
Co-authored-by: Filippo A. E. Nuccio <filippo.nuccio@univ-st-etienne.fr>
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@mans0954 I let you check all my comments, then please ping me so that I can come back for another round of review.

mathlib-bors bot pushed a commit that referenced this pull request Oct 14, 2025
… a single ring of scalars (#29342)

Currently the definition of Absolutely Convex in Mathlib is a little unexpected:
```
def AbsConvex (s : Set E) : Prop := Balanced 𝕜 s ∧ Convex ℝ s
```
At the time this definition was formulated, Mathlib's definition of `Convex` required the scalars to be an `OrderedSemiring` whereas the definition of `Balanced` required the scalars to be a `SeminormedRing`. Mathlib didn't  have a concept of a semi-normed ordered ring, so a set was defined as `AbsConvex` if it is balanced over a `SeminormedRing` `𝕜` and convex over `ℝ`.

Recently the requirements for the definition of `Convex` have been relaxed (#24392, #20595) so it is now possible to use a single scalar ring in common with the literature.

Previous discussion:

- #17029 (comment)
- #26345 (comment)
@mathlib4-merge-conflict-bot mathlib4-merge-conflict-bot added the merge-conflict The PR has a merge conflict with master, and needs manual merging. (this label is managed by a bot) label Oct 14, 2025
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This pull request has conflicts, please merge master and resolve them.

Jlh18 pushed a commit to Jlh18/mathlib4 that referenced this pull request Oct 24, 2025
… a single ring of scalars (leanprover-community#29342)

Currently the definition of Absolutely Convex in Mathlib is a little unexpected:
```
def AbsConvex (s : Set E) : Prop := Balanced 𝕜 s ∧ Convex ℝ s
```
At the time this definition was formulated, Mathlib's definition of `Convex` required the scalars to be an `OrderedSemiring` whereas the definition of `Balanced` required the scalars to be a `SeminormedRing`. Mathlib didn't  have a concept of a semi-normed ordered ring, so a set was defined as `AbsConvex` if it is balanced over a `SeminormedRing` `𝕜` and convex over `ℝ`.

Recently the requirements for the definition of `Convex` have been relaxed (leanprover-community#24392, leanprover-community#20595) so it is now possible to use a single scalar ring in common with the literature.

Previous discussion:

- leanprover-community#17029 (comment)
- leanprover-community#26345 (comment)
BeibeiX0 pushed a commit to BeibeiX0/mathlib4 that referenced this pull request Nov 7, 2025
… a single ring of scalars (leanprover-community#29342)

Currently the definition of Absolutely Convex in Mathlib is a little unexpected:
```
def AbsConvex (s : Set E) : Prop := Balanced 𝕜 s ∧ Convex ℝ s
```
At the time this definition was formulated, Mathlib's definition of `Convex` required the scalars to be an `OrderedSemiring` whereas the definition of `Balanced` required the scalars to be a `SeminormedRing`. Mathlib didn't  have a concept of a semi-normed ordered ring, so a set was defined as `AbsConvex` if it is balanced over a `SeminormedRing` `𝕜` and convex over `ℝ`.

Recently the requirements for the definition of `Convex` have been relaxed (leanprover-community#24392, leanprover-community#20595) so it is now possible to use a single scalar ring in common with the literature.

Previous discussion:

- leanprover-community#17029 (comment)
- leanprover-community#26345 (comment)
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@mans0954 Are you planning to keep on working on this PR?

@faenuccio faenuccio self-assigned this Dec 23, 2025
@j-loreaux j-loreaux self-assigned this Dec 24, 2025
@github-actions github-actions bot removed the merge-conflict The PR has a merge conflict with master, and needs manual merging. (this label is managed by a bot) label Jan 4, 2026
@mathlib4-merge-conflict-bot mathlib4-merge-conflict-bot added the merge-conflict The PR has a merge conflict with master, and needs manual merging. (this label is managed by a bot) label Jan 8, 2026
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This pull request has conflicts, please merge master and resolve them.

@vihdzp vihdzp added the please-adopt Inactive PR (would be valuable to adopt) label Jan 11, 2026
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