Module: Mathlib.RepresentationTheory.Homological.GroupCohomology.Hilbert90

Goal state before:
pp: case refine_2
K L : Type
inst✝¹⁶ : Field K
inst✝¹⁵ : Field L
inst✝¹⁴ : Algebra K L
inst✝¹³ : FiniteDimensional K L
inst✝¹² : IsGalois K L
inst✝¹¹ : IsCyclic Gal(L/K)
g : Gal(L/K)
A : Type u_1
B : Type u_2
inst✝¹⁰ : CommRing A
inst✝⁹ : CommRing B
inst✝⁸ : Algebra A B
inst✝⁷ : Algebra A L
inst✝⁶ : Algebra A K
inst✝⁵ : Algebra B L
inst✝⁴ : IsScalarTower A B L
inst✝³ : IsScalarTower A K L
inst✝² : IsFractionRing A K
inst✝¹ : IsDomain A
inst✝ : IsIntegralClosure B A L
hg : ∀ (x : Gal(L/K)), x ∈ Subgroup.zpowers g
η : B
hη : (Algebra.norm K) ((algebraMap B L) η) = 1
this✝¹ : Module.IsTorsionFree A L
this✝ : IsLocalization (Algebra.algebraMapSubmonoid B A⁰) L
η' : Lˣ := Units.mk0 ((algebraMap B L) η) ⋯
ε : Lˣ
a : B
b : ↥(Algebra.algebraMapSubmonoid B A⁰)
h : IsLocalization.mk' L a b = ↑ε
t : A
ht : t ∈ ↑A⁰
ht' : (algebraMap A B) t = ↑b
this : t • IsLocalization.mk' L a b = (algebraMap B L) a
hε : (algebraMap B L) η * g (IsLocalization.mk' L a b) = IsLocalization.mk' L a b
⊢ η * ((galRestrict A K L B) g) a = a

pp: case refine_2
K L : Type
inst✝¹⁶ : Field K
inst✝¹⁵ : Field L
inst✝¹⁴ : Algebra K L
inst✝¹³ : FiniteDimensional K L
inst✝¹² : IsGalois K L
inst✝¹¹ : IsCyclic Gal(L/K)
g : Gal(L/K)
A : Type u_1
B : Type u_2
inst✝¹⁰ : CommRing A
inst✝⁹ : CommRing B
inst✝⁸ : Algebra A B
inst✝⁷ : Algebra A L
inst✝⁶ : Algebra A K
inst✝⁵ : Algebra B L
inst✝⁴ : IsScalarTower A B L
inst✝³ : IsScalarTower A K L
inst✝² : IsFractionRing A K
inst✝¹ : IsDomain A
inst✝ : IsIntegralClosure B A L
hg : ∀ (x : Gal(L/K)), x ∈ Subgroup.zpowers g
η : B
hη : (Algebra.norm K) ((algebraMap B L) η) = 1
this✝¹ : Module.IsTorsionFree A L
this✝ : IsLocalization (Algebra.algebraMapSubmonoid B A⁰) L
η' : Lˣ := Units.mk0 ((algebraMap B L) η) ⋯
ε : Lˣ
a : B
b : ↥(Algebra.algebraMapSubmonoid B A⁰)
h : IsLocalization.mk' L a b = ↑ε
t : A
ht : t ∈ ↑A⁰
ht' : (algebraMap A B) t = ↑b
this : t • IsLocalization.mk' L a b = (algebraMap B L) a
hε : (algebraMap B L) η = IsLocalization.mk' L a b / g (IsLocalization.mk' L a b)
⊢ g (IsLocalization.mk' L a b) ≠ 0

Tactic:
· replace hε := congr_arg (t • ·) hε
      rw [Algebra.smul_def, mul_left_comm, ← Algebra.smul_def t, ← g.toAlgHom_apply,
        ← AlgHom.map_smul_of_tower, this] at hε
      apply IsIntegralClosure.algebraMap_injective B A L
      rw [map_mul, ← hε]
      congr 1
      exact algebraMap_galRestrictHom_apply A K L B g a

Goal state after:
case refine_2
K L : Type
inst✝¹⁶ : Field K
inst✝¹⁵ : Field L
inst✝¹⁴ : Algebra K L
inst✝¹³ : FiniteDimensional K L
inst✝¹² : IsGalois K L
inst✝¹¹ : IsCyclic Gal(L/K)
g : Gal(L/K)
A : Type u_1
B : Type u_2
inst✝¹⁰ : CommRing A
inst✝⁹ : CommRing B
inst✝⁸ : Algebra A B
inst✝⁷ : Algebra A L
inst✝⁶ : Algebra A K
inst✝⁵ : Algebra B L
inst✝⁴ : IsScalarTower A B L
inst✝³ : IsScalarTower A K L
inst✝² : IsFractionRing A K
inst✝¹ : IsDomain A
inst✝ : IsIntegralClosure B A L
hg : ∀ (x : Gal(L/K)), x ∈ Subgroup.zpowers g
η : B
hη : (Algebra.norm K) ((algebraMap B L) η) = 1
this✝¹ : Module.IsTorsionFree A L
this✝ : IsLocalization (Algebra.algebraMapSubmonoid B A⁰) L
η' : Lˣ := Units.mk0 ((algebraMap B L) η) ⋯
ε : Lˣ
a : B
b : ↥(Algebra.algebraMapSubmonoid B A⁰)
h : IsLocalization.mk' L a b = ↑ε
t : A
ht : t ∈ ↑A⁰
ht' : (algebraMap A B) t = ↑b
this : t • IsLocalization.mk' L a b = (algebraMap B L) a
hε : (algebraMap B L) η = IsLocalization.mk' L a b / g (IsLocalization.mk' L a b)
⊢ g (IsLocalization.mk' L a b) ≠ 0