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
@[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 ℕ := 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 →ₜ* 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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