Module: Mathlib.RingTheory.DedekindDomain.Different

Goal state before:
pp: case refine_1
A : Type u_1
B : Type u_3
inst✝¹² : CommRing A
inst✝¹¹ : CommRing B
inst✝¹⁰ : Algebra A B
inst✝⁹ : IsDomain A
inst✝⁸ : IsDedekindDomain A
inst✝⁷ : IsDedekindDomain B
inst✝⁶ : IsTorsionFree A B
inst✝⁵ : Module.Finite A B
inst✝⁴ : Algebra.IsSeparable (FractionRing A) (FractionRing B)
p : Ideal A
inst✝³ : p.IsMaximal
P Q : Ideal B
inst✝² : P.IsMaximal
inst✝¹ : P.LiesOver p
hPQ : IsCoprime P Q
hP : P * Q = Ideal.map (algebraMap A B) p
inst✝ : Algebra.IsSeparable (A ⧸ p) (B ⧸ P)
this✝¹ : Algebra (A ⧸ p) (B ⧸ Q) := Ideal.Quotient.algebraQuotientOfLEComap ⋯
this✝ : IsScalarTower A (A ⧸ p) (B ⧸ Q)
this : Module.Finite (A ⧸ p) (B ⧸ Q)
e : (B ⧸ Ideal.map (algebraMap A B) p) ≃ₐ[A ⧸ p] (B ⧸ P) × B ⧸ Q :=
  let __spread.0 := (Ideal.quotEquivOfEq ⋯).trans (P.quotientMulEquivQuotientProd Q hPQ);
  { toEquiv := __spread.0.toEquiv, map_mul' := ⋯, map_add' := ⋯, commutes' := ⋯ }
x : B ⧸ P
hx : (Algebra.trace (A ⧸ p) (B ⧸ P)) x ≠ 0
y : B
hy : (Ideal.Quotient.mk (Ideal.map (algebraMap A B) p)) y = e.symm (x, 0)
⊢ y ∈ Q

pp: case refine_2
A : Type u_1
B : Type u_3
inst✝¹² : CommRing A
inst✝¹¹ : CommRing B
inst✝¹⁰ : Algebra A B
inst✝⁹ : IsDomain A
inst✝⁸ : IsDedekindDomain A
inst✝⁷ : IsDedekindDomain B
inst✝⁶ : IsTorsionFree A B
inst✝⁵ : Module.Finite A B
inst✝⁴ : Algebra.IsSeparable (FractionRing A) (FractionRing B)
p : Ideal A
inst✝³ : p.IsMaximal
P Q : Ideal B
inst✝² : P.IsMaximal
inst✝¹ : P.LiesOver p
hPQ : IsCoprime P Q
hP : P * Q = Ideal.map (algebraMap A B) p
inst✝ : Algebra.IsSeparable (A ⧸ p) (B ⧸ P)
this✝¹ : Algebra (A ⧸ p) (B ⧸ Q) := Ideal.Quotient.algebraQuotientOfLEComap ⋯
this✝ : IsScalarTower A (A ⧸ p) (B ⧸ Q)
this : Module.Finite (A ⧸ p) (B ⧸ Q)
e : (B ⧸ Ideal.map (algebraMap A B) p) ≃ₐ[A ⧸ p] (B ⧸ P) × B ⧸ Q :=
  let __spread.0 := (Ideal.quotEquivOfEq ⋯).trans (P.quotientMulEquivQuotientProd Q hPQ);
  { toEquiv := __spread.0.toEquiv, map_mul' := ⋯, map_add' := ⋯, commutes' := ⋯ }
x : B ⧸ P
hx : (Algebra.trace (A ⧸ p) (B ⧸ P)) x ≠ 0
y : B
hy : (Ideal.Quotient.mk (Ideal.map (algebraMap A B) p)) y = e.symm (x, 0)
⊢ (intTrace A B) y ∉ p

Tactic:
· have := congr((e $hy).2)
    simp at this
    simpa [e, Ideal.Quotient.eq_zero_iff_mem] using this

Goal state after:
case refine_2
A : Type u_1
B : Type u_3
inst✝¹² : CommRing A
inst✝¹¹ : CommRing B
inst✝¹⁰ : Algebra A B
inst✝⁹ : IsDomain A
inst✝⁸ : IsDedekindDomain A
inst✝⁷ : IsDedekindDomain B
inst✝⁶ : IsTorsionFree A B
inst✝⁵ : Module.Finite A B
inst✝⁴ : Algebra.IsSeparable (FractionRing A) (FractionRing B)
p : Ideal A
inst✝³ : p.IsMaximal
P Q : Ideal B
inst✝² : P.IsMaximal
inst✝¹ : P.LiesOver p
hPQ : IsCoprime P Q
hP : P * Q = Ideal.map (algebraMap A B) p
inst✝ : Algebra.IsSeparable (A ⧸ p) (B ⧸ P)
this✝¹ : Algebra (A ⧸ p) (B ⧸ Q) := Ideal.Quotient.algebraQuotientOfLEComap ⋯
this✝ : IsScalarTower A (A ⧸ p) (B ⧸ Q)
this : Module.Finite (A ⧸ p) (B ⧸ Q)
e : (B ⧸ Ideal.map (algebraMap A B) p) ≃ₐ[A ⧸ p] (B ⧸ P) × B ⧸ Q :=
  let __spread.0 := (Ideal.quotEquivOfEq ⋯).trans (P.quotientMulEquivQuotientProd Q hPQ);
  { toEquiv := __spread.0.toEquiv, map_mul' := ⋯, map_add' := ⋯, commutes' := ⋯ }
x : B ⧸ P
hx : (Algebra.trace (A ⧸ p) (B ⧸ P)) x ≠ 0
y : B
hy : (Ideal.Quotient.mk (Ideal.map (algebraMap A B) p)) y = e.symm (x, 0)
⊢ (intTrace A B) y ∉ p