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Project-declaredLean 4.32.0 · mathlib@249c48c2

Comm Group no compact automorphisms

CommGroup.no_compact_automorphisms

Plain-language statement

A connected compact Hausdorff abelian topological group does not admit a nontrivial compact group of automorphisms.

Exact Lean statement

@[to_additive]
theorem CommGroup.no_compact_automorphisms
    {A : Type*} [CommGroup A] [TopologicalSpace A] [IsTopologicalGroup A]
    [ConnectedSpace A] [CompactSpace A] [T2Space A] (K : Subgroup (ContinuousMonoidHom A A))
    (hK : IsCompact (K : Set (ContinuousMonoidHom A A))) :
    K = ⊥

Formal artifact

Lean source

Canonical source
Full Lean sourceLean 4
@[to_additive]theorem CommGroup.no_compact_automorphisms    {A : Type*} [CommGroup A] [TopologicalSpace A] [IsTopologicalGroup A]    [ConnectedSpace A] [CompactSpace A] [T2Space A] (K : Subgroup (ContinuousMonoidHom A A))    (hK : IsCompact (K : Set (ContinuousMonoidHom A A))) :    K =:= by  have A_rootable : RootableBy A  := Group.rootable A  rw [eq_bot_iff]  intro f hf  ext a  rw [ContinuousMonoidHom.one_toFun]  by_contra! ha  let U : Set A := {f a}ᶜ  have hU : IsOpen U := isOpen_compl_singleton  have hU1 : 1  U := ha.symm  let W : Set (A * A) := {f | Set.MapsTo f Set.univ U}  have hW : IsOpen W :=    (ContinuousMonoidHom.isInducing_toContinuousMap A A).continuous.isOpen_preimage _      (ContinuousMap.isOpen_setOf_mapsTo isCompact_univ hU)  have hW1 : 1  W := by simpa [W]  replace hW1 : W  nhds 1 := hW.mem_nhds hW1  have : CompactSpace K := isCompact_iff_compactSpace.mp hK  obtain n, hn0, hnf :=    (mapClusterPt_iff_frequently.mp (mapClusterPt_one_atTop_pow f, hf) (Subtype.val ⁻¹' W)    (continuousAt_subtype_val.preimage_mem_nhds (by exact hW1))).forall_exists_of_atTop 1  replace hn0 : n  0 := by grind  rw [Set.mem_preimage, Subgroup.coe_pow, Subtype.coe_mk,    Set.mem_setOf_eq, Set.mapsTo_univ_iff,  Set.range_subset_iff] at hnf  change (f ^ n).range  U at hnf  suffices f.range  (f ^ n).range by    exact (Set.Subset.trans this hnf) a, rfl rfl  rintro - b, rfl  use RootableBy.root b n  simp [ContinuousMonoidHom.pow_apply,  map_pow, RootableBy.root_cancel b hn0]
Project
Fermat's Last Theorem
License
Apache-2.0
Commit
8dd808888295
Source
FLT/Patching/Utils/CompactHausdorffRings.lean:91-124

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Related declarations

Project-declaredLean 4.32.0

Eq finsum quotient out of bij On

AbstractHeckeOperator.eq_finsum_quotient_out_of_bijOn'

Plain-language statement

If a is fixed by V then ∑ᶠ g ∈ s, g • a is independent of the choice s of coset representatives in G for a subset of G ⧸ V

number theoryarithmetic geometryFermat's Last Theorem

Source project: Fermat's Last Theorem

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