Module

Compactness.lean

Nyll.ProCGroups.NormalSubgroups.SimpleQuotients.Compactness
2 declarations indexed from sourceView source ↗

Compactness for intersections above a simple-quotient kernel

This module upgrades a finite-intersection property for closed normal subgroups of a compact group to the corresponding arbitrary-intersection property.

Declarations

ProCGroups.NormalSubgroups.maximal_open_normal_intersections_compactness_step

Compactness step: if the closed normal subgroups satisfying \(M \sqcup K = \top\) are already stable under finite intersections, then they are stable under arbitrary intersections.

Source context 2 commands

Surrounding namespaces, section variables, and local commands at this declaration.

namespace ProCGroups.NormalSubgroups
universe u
theorem maximal_open_normal_intersections_compactness_step
    {G : Type u} [Group G] [TopologicalSpace G] [IsTopologicalGroup G] [CompactSpace G]
    (K : Subgroup G) [K.Normal] (hKclosed : IsClosed (K : Set G))
    (𝓜 : Set (Subgroup G))
    (hMclosed : ∀ M ∈ 𝓜, IsClosed (M : Set G))
    (hfinite :
      ∀ S : Set (Subgroup G), S.Finite → S ⊆ 𝓜 → sInf S ⊔ K = ⊤) :
    sInf 𝓜 ⊔ K = ⊤
ProCGroups.NormalSubgroups.maximal_open_normal_intersections_nonabelian_simple

Maximal open normal subgroups with a fixed nonabelian simple quotient are closed under arbitrary intersections.

Source context 2 commands

Surrounding namespaces, section variables, and local commands at this declaration.

namespace ProCGroups.NormalSubgroups
universe u
theorem maximal_open_normal_intersections_nonabelian_simple
    {G : Type u} [Group G] [TopologicalSpace G] [IsTopologicalGroup G] [CompactSpace G]
    (K : Subgroup G) [K.Normal] [IsSimpleGroup (G ⧸ K)]
    (hquotNoncomm : ProCGroups.IsNoncommutativeGroup (G ⧸ K))
    (hKclosed : IsClosed (K : Set G))
    (𝓜 : Set (Subgroup G))
    (hMnormal : ∀ M ∈ 𝓜, M.Normal)
    (hMclosed : ∀ M ∈ 𝓜, IsClosed (M : Set G))
    (hMtop : ∀ M ∈ 𝓜, M ⊔ K = ⊤) :
    sInf 𝓜 ⊔ K = ⊤