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feat: continuous linear equivalence between continuous - and 𝕜-linear functionals (in either the strong or weak-⋆ topologies)#34728

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feat: continuous linear equivalence between continuous - and 𝕜-linear functionals (in either the strong or weak-⋆ topologies)#34728
j-loreaux wants to merge 15 commits intoleanprover-community:masterfrom
j-loreaux:WeakDual-extend

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@j-loreaux j-loreaux commented Feb 2, 2026

This realizes the map StrongDual.extendRCLikeₗ, after pre- and post-composing so that it is an equivalence between the weak duals, as a continuous linear equivalence.

In addition, when the space is a topological vector space, we realize StrongDual.extendRCLikeₗ as a continuous linear equivalence between the strong duals.


The placement in Analysis/Normed/Module/WeakDual seems suboptimal because this has nothing to do with the norm. This is because WeakDual.toStrongDual is already in this file, which should probably be moved to Topology/Algebra/Module/WeakDual. However, even if that moves, the declarations added in this PR cannot easily go with it because they involve RCLike. Potentially, they could move to Analysis/RCLike/Extend if that file gained the Topology/Algebra/Module/WeakDual import.


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github-actions bot commented Feb 2, 2026

PR summary 9d0ea7dd98

Import changes for modified files

Dependency changes

File Base Count Head Count Change
Mathlib.Analysis.Normed.Module.RCLike.Extend 1713 1718 +5 (+0.29%)
Mathlib.Analysis.Normed.Module.WeakDual 2159 2160 +1 (+0.05%)
Import changes for all files
Files Import difference
4 files Mathlib.Analysis.Normed.Algebra.Basic Mathlib.Analysis.Normed.Module.Dual Mathlib.Analysis.Normed.Module.HahnBanach Mathlib.Analysis.Normed.Module.WeakDual
1
Mathlib.Analysis.Normed.Module.RCLike.Extend 5

Declarations diff

+ _root_.StrongDual.toWeakDual_extendRCLikeₗ_apply
+ _root_.WeakBilin.continuous_of_continuous_eval_re
+ continuous_of_continuous_eval_re
+ extendRCLikeL_apply_apply
+ extendRCLikeL_symm_apply_apply
+ toContinuousLinearEquiv_extendRCLikeₗᵢ
+ toStrongDual_extendRCLikeL_apply
++ extendRCLikeL

You can run this locally as follows
## summary with just the declaration names:
./scripts/pr_summary/declarations_diff.sh <optional_commit>

## more verbose report:
./scripts/pr_summary/declarations_diff.sh long <optional_commit>

The doc-module for scripts/pr_summary/declarations_diff.sh contains some details about this script.


Increase in tech debt: (relative, absolute) = (1.00, 0.00)
Current number Change Type
10188 1 backward.isDefEq

Current commit d27852e8ac
Reference commit 9d0ea7dd98

You can run this locally as

./scripts/reporting/technical-debt-metrics.sh pr_summary
  • The relative value is the weighted sum of the differences with weight given by the inverse of the current value of the statistic.
  • The absolute value is the relative value divided by the total sum of the inverses of the current values (i.e. the weighted average of the differences).

@github-actions github-actions bot added the t-analysis Analysis (normed *, calculus) label Feb 2, 2026
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github-actions bot commented Feb 2, 2026

✅ PR Title Formatted Correctly

The title of this PR has been updated to match our commit style conventions.
Thank you!

@j-loreaux j-loreaux changed the title WeakDual-extend feat: continuous linear equivalence between continuous and 𝕜-linear functionals, when equipped with the weak⋆-topology Feb 2, 2026
@j-loreaux j-loreaux changed the title feat: continuous linear equivalence between continuous and 𝕜-linear functionals, when equipped with the weak⋆-topology feat: continuous linear equivalence between continuous - and 𝕜-linear functionals, when equipped with the weak⋆-topology Feb 2, 2026
@mathlib4-dependent-issues-bot mathlib4-dependent-issues-bot added the blocked-by-other-PR This PR depends on another PR (this label is automatically managed by a bot) label Feb 2, 2026
@mathlib-merge-conflicts mathlib-merge-conflicts 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 Feb 18, 2026
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This pull request has conflicts, please merge master and resolve them.

@mathlib-dependent-issues mathlib-dependent-issues bot removed the blocked-by-other-PR This PR depends on another PR (this label is automatically managed by a bot) label Feb 25, 2026
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@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 Mar 9, 2026
@j-loreaux j-loreaux changed the title feat: continuous linear equivalence between continuous - and 𝕜-linear functionals, when equipped with the weak⋆-topology feat: continuous linear equivalence between continuous - and 𝕜-linear functionals (in either the strong or weak-⋆ topologies) Mar 9, 2026
@j-loreaux j-loreaux requested a review from urkud March 10, 2026 04:16
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@urkud this is the follow up to the PR containing the StrongDual.extendRCLike refactor. Here I provide the bundlings StrongDual ℝ F ≃L[ℝ] StrongDual 𝕜 F and WeakDual ℝ F ≃L[ℝ] WeakDual 𝕜 F.

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Not strictly related, but do we agree that the sentence "It would be possible to use LinearMap.mkContinuous here, but we would need to know that the continuity of fr implies it has bounded norm and we want to avoid that dependency here." in the docstring of StrongDual.extendRCLike is misleading because there is no longer any norm around?

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@ADedecker Sure, I can delete it in this PR if you would like, or do it in a separate one.

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