Module: Mathlib.RingTheory.Invariant.Profinite

Goal state before:
pp: case refine_1
A : Type u_1
B : Type u_2
inst✝¹⁵ : CommRing A
inst✝¹⁴ : CommRing B
inst✝¹³ : Algebra A B
G : Type u
inst✝¹² : Group G
inst✝¹¹ : MulSemiringAction G B
inst✝¹⁰ : SMulCommClass G A B
inst✝⁹ : TopologicalSpace G
inst✝⁸ : CompactSpace G
inst✝⁷ : TotallyDisconnectedSpace G
inst✝⁶ : IsTopologicalGroup G
inst✝⁵ : TopologicalSpace B
inst✝⁴ : DiscreteTopology B
inst✝³ : ContinuousSMul G B
P : Ideal A
Q : Ideal B
inst✝² : Q.IsPrime
inst✝¹ : Q.LiesOver P
inst✝ : Algebra.IsInvariant A B G
σ : (B ⧸ Q) ≃ₐ[A ⧸ P] B ⧸ Q
B' : (G : Type ?u.58) → [inst : Monoid G] → [inst_1 : MulSemiringAction G B] → [SMulCommClass G A B] → Subalgebra A B :=
  FixedPoints.subalgebra A B
s : (j : OpenNormalSubgroup G) → (stabilizerHomSurjectiveAuxFunctor P Q σ).obj j
hs : s ∈ (stabilizerHomSurjectiveAuxFunctor P Q σ).sections
a : ↑(ProfiniteGrp.of G).toProfinite.toTop :=
  (ProfiniteGrp.Hom.hom (ProfiniteGrp.of G).isoLimittoFiniteQuotientFunctor.inv) ⟨fun N ↦ ↑↑(s N), ⋯⟩
this : ∀ (N : OpenNormalSubgroup G), ↑a = ↑↑(s N)
⊢ a ∈ MulAction.stabilizer G Q

pp: case refine_2
A : Type u_1
B : Type u_2
inst✝¹⁵ : CommRing A
inst✝¹⁴ : CommRing B
inst✝¹³ : Algebra A B
G : Type u
inst✝¹² : Group G
inst✝¹¹ : MulSemiringAction G B
inst✝¹⁰ : SMulCommClass G A B
inst✝⁹ : TopologicalSpace G
inst✝⁸ : CompactSpace G
inst✝⁷ : TotallyDisconnectedSpace G
inst✝⁶ : IsTopologicalGroup G
inst✝⁵ : TopologicalSpace B
inst✝⁴ : DiscreteTopology B
inst✝³ : ContinuousSMul G B
P : Ideal A
Q : Ideal B
inst✝² : Q.IsPrime
inst✝¹ : Q.LiesOver P
inst✝ : Algebra.IsInvariant A B G
σ : (B ⧸ Q) ≃ₐ[A ⧸ P] B ⧸ Q
B' : (G : Type ?u.58) → [inst : Monoid G] → [inst_1 : MulSemiringAction G B] → [SMulCommClass G A B] → Subalgebra A B :=
  FixedPoints.subalgebra A B
s : (j : OpenNormalSubgroup G) → (stabilizerHomSurjectiveAuxFunctor P Q σ).obj j
hs : s ∈ (stabilizerHomSurjectiveAuxFunctor P Q σ).sections
a : ↑(ProfiniteGrp.of G).toProfinite.toTop :=
  (ProfiniteGrp.Hom.hom (ProfiniteGrp.of G).isoLimittoFiniteQuotientFunctor.inv) ⟨fun N ↦ ↑↑(s N), ⋯⟩
this : ∀ (N : OpenNormalSubgroup G), ↑a = ↑↑(s N)
⊢ (stabilizerHom Q P G) ⟨a, ?refine_1⟩ = σ

Tactic:
· ext x
    obtain ⟨N, hN⟩ := ProfiniteGrp.exist_openNormalSubgroup_sub_open_nhds_of_one
      (stabilizer_isOpen G x) (one_mem _)
    lift x to B' N.1.1 using fun g ↦ hN g.2
    change x ∈ (a • Q).under (B' N.1.1) ↔ x ∈ Q.under (B' N.1.1)
    rw [← (s N).1.2]
    simp only [Ideal.comap_comap, Ideal.pointwise_smul_eq_comap, ← Ideal.comap_coe
          (F := RingEquiv _ _)]
    congr! 2
    ext y
    rw [← this]
    rfl

Goal state after:
case refine_2
A : Type u_1
B : Type u_2
inst✝¹⁵ : CommRing A
inst✝¹⁴ : CommRing B
inst✝¹³ : Algebra A B
G : Type u
inst✝¹² : Group G
inst✝¹¹ : MulSemiringAction G B
inst✝¹⁰ : SMulCommClass G A B
inst✝⁹ : TopologicalSpace G
inst✝⁸ : CompactSpace G
inst✝⁷ : TotallyDisconnectedSpace G
inst✝⁶ : IsTopologicalGroup G
inst✝⁵ : TopologicalSpace B
inst✝⁴ : DiscreteTopology B
inst✝³ : ContinuousSMul G B
P : Ideal A
Q : Ideal B
inst✝² : Q.IsPrime
inst✝¹ : Q.LiesOver P
inst✝ : Algebra.IsInvariant A B G
σ : (B ⧸ Q) ≃ₐ[A ⧸ P] B ⧸ Q
B' : (G : Type u) → [inst : Monoid G] → [inst_1 : MulSemiringAction G B] → [SMulCommClass G A B] → Subalgebra A B :=
  FixedPoints.subalgebra A B
s : (j : OpenNormalSubgroup G) → (stabilizerHomSurjectiveAuxFunctor P Q σ).obj j
hs : s ∈ (stabilizerHomSurjectiveAuxFunctor P Q σ).sections
a : ↑(ProfiniteGrp.of G).toProfinite.toTop :=
  (ProfiniteGrp.Hom.hom (ProfiniteGrp.of G).isoLimittoFiniteQuotientFunctor.inv) ⟨fun N ↦ ↑↑(s N), ⋯⟩
this : ∀ (N : OpenNormalSubgroup G), ↑a = ↑↑(s N)
⊢ (stabilizerHom Q P G) ⟨a, ⋯⟩ = σ