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feat: Amenable monoid actions #7395

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feat: Amenable monoid actions #7395

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@matthias567 matthias567 commented Sep 27, 2023


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@matthias567 matthias567 added the awaiting-review The author would like community review of the PR label Sep 27, 2023
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matthias567 and others added 3 commits September 27, 2023 12:25
Co-authored-by: sgouezel <sebastien.gouezel@univ-rennes1.fr>
Co-authored-by: sgouezel <sebastien.gouezel@univ-rennes1.fr>
@matthias567 matthias567 added awaiting-author A reviewer has asked the author a question or requested changes and removed awaiting-review The author would like community review of the PR labels Sep 27, 2023
@matthias567 matthias567 added awaiting-review The author would like community review of the PR and removed awaiting-author A reviewer has asked the author a question or requested changes labels Sep 28, 2023
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What about redefining ProbabilityMeasure as extending both Measure and Mean? (mostly a question for the resident measure theorists)

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matthias567 and others added 2 commits September 28, 2023 11:14
Co-authored-by: Yaël Dillies <yael.dillies@gmail.com>
matthias567 and others added 5 commits October 16, 2023 21:05
Co-authored-by: Eric Wieser <wieser.eric@gmail.com>
Co-authored-by: Eric Wieser <wieser.eric@gmail.com>
Co-authored-by: Eric Wieser <wieser.eric@gmail.com>
@sgouezel sgouezel added the new-contributor This PR was made by a contributor with fewer than 5 merged PRs. Welcome to the community! label Nov 5, 2023
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Sorry for the review delay. Overall, this looks good to me, although I have minor nitpicky comments (which is perfectly normal).

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/-- For amenable actions, we can pick an invariant mean -/
noncomputable def invmean_of_amenable (h: Amenable α G) :
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Suggested change
noncomputable def invmean_of_amenable (h: Amenable α G) :
noncomputable def invariantMean_of_amenable (h : Amenable α G) :

If you have made Amenable a typeclass, though, I would change this to invMean [Amenable α G], where the difference would be necessary to emphasize that it's not the same thing (i.e., we are picking some choice, vs. the space of all invariant means).

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Yes, I'll do this. However, this breaks invMean. I might need some help in fixing that (in the commit #8b3e8d7de, this is the comment at the end of the file)

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@sgouezel sgouezel added awaiting-author A reviewer has asked the author a question or requested changes t-measure-probability Measure theory / Probability theory t-dynamics Dynamical Systems and removed awaiting-review The author would like community review of the PR labels Nov 8, 2023
@matthias567 matthias567 added bug Something isn't working help-wanted The author needs attention to resolve issues awaiting-review The author would like community review of the PR and removed awaiting-author A reviewer has asked the author a question or requested changes bug Something isn't working labels Nov 14, 2023
@YaelDillies YaelDillies changed the title feat(GroupTheory/GroupActions/amenable): add definition of amenable monoid actions feat: Amenable monoid actions Nov 14, 2023
@leanprover-community-mathlib4-bot leanprover-community-mathlib4-bot added the merge-conflict The PR has a merge conflict with master, and needs manual merging. label Apr 20, 2024
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