-- Mathlib/RingTheory/Trace/Quotient.lean
/-- The trace map on `B → A` coincides with the trace map on `B⧸pB → A⧸p`. -/
lemma Algebra.trace_quotient_eq_of_isDedekindDomain (x) [IsDedekindDomain R] [IsDomain S]
    [NoZeroSMulDivisors R S] [Module.Finite R S] [IsIntegrallyClosed S] :
    Algebra.trace (R ⧸ p) (S ⧸ pS) (Ideal.Quotient.mk pS x) =
      Ideal.Quotient.mk p (Algebra.intTrace R S x)

Proof state:
case intro.intro
R : Type u_1
S : Type u_2
inst✝⁸ : CommRing R
inst✝⁷ : CommRing S
inst✝⁶ : Algebra R S
p : Ideal R
inst✝⁵ : p.IsMaximal
x✝ : S
inst✝⁴ : IsDedekindDomain R
inst✝³ : IsDomain S
inst✝² : NoZeroSMulDivisors R S
inst✝¹ : Module.Finite R S
inst✝ : IsIntegrallyClosed S
Rₚ : Type u_1 := Localization.AtPrime p
Sₚ : Type u_2 := Localization (algebraMapSubmonoid S p.primeCompl)
this✝² : Algebra Rₚ Sₚ := localizationAlgebra p.primeCompl S
this✝¹ : IsScalarTower R Rₚ Sₚ
this✝ : IsLocalization (Submonoid.map (algebraMap R S) p.primeCompl) Sₚ
e : algebraMapSubmonoid S p.primeCompl ≤ S⁰
this : IsDomain Sₚ
x : R
s : ↥p.primeCompl
hx : (algebraMap Rₚ Sₚ) (IsLocalization.mk' Rₚ x s) = 0
⊢ IsLocalization.mk' Rₚ x s = 0

Tactic:
simp only [Sₚ, RingHom.algebraMap_toAlgebra, IsLocalization.map_mk',
  IsLocalization.mk'_eq_zero_iff, mul_eq_zero, Subtype.exists, exists_prop] at hx ⊢

Result:
case intro.intro
R : Type u_1
S : Type u_2
inst✝⁸ : CommRing R
inst✝⁷ : CommRing S
inst✝⁶ : Algebra R S
p : Ideal R
inst✝⁵ : p.IsMaximal
x✝ : S
inst✝⁴ : IsDedekindDomain R
inst✝³ : IsDomain S
inst✝² : NoZeroSMulDivisors R S
inst✝¹ : Module.Finite R S
inst✝ : IsIntegrallyClosed S
Rₚ : Type u_1 := Localization.AtPrime p
Sₚ : Type u_2 := Localization (algebraMapSubmonoid S p.primeCompl)
this✝² : Algebra Rₚ Sₚ := localizationAlgebra p.primeCompl S
this✝¹ : IsScalarTower R Rₚ Sₚ
this✝ : IsLocalization (Submonoid.map (algebraMap R S) p.primeCompl) Sₚ
e : algebraMapSubmonoid S p.primeCompl ≤ S⁰
this : IsDomain Sₚ
x : R
s : ↥p.primeCompl
hx : ∃ a ∈ algebraMapSubmonoid S p.primeCompl, a = 0 ∨ (algebraMap R S) x = 0
⊢ ∃ a ∈ p.primeCompl, a = 0 ∨ x = 0

Proof state:
R : Type u_1
S : Type u_2
inst✝⁸ : CommRing R
inst✝⁷ : CommRing S
inst✝⁶ : Algebra R S
p : Ideal R
inst✝⁵ : p.IsMaximal
x : S
inst✝⁴ : IsDedekindDomain R
inst✝³ : IsDomain S
inst✝² : NoZeroSMulDivisors R S
inst✝¹ : Module.Finite R S
inst✝ : IsIntegrallyClosed S
Rₚ : Type u_1 := Localization.AtPrime p
Sₚ : Type u_2 := Localization (algebraMapSubmonoid S p.primeCompl)
this✝⁷ : Algebra Rₚ Sₚ := localizationAlgebra p.primeCompl S
this✝⁶ : IsScalarTower R Rₚ Sₚ
this✝⁵ : IsLocalization (Submonoid.map (algebraMap R S) p.primeCompl) Sₚ
e : algebraMapSubmonoid S p.primeCompl ≤ S⁰
this✝⁴ : IsDomain Sₚ
this✝³ : NoZeroSMulDivisors Rₚ Sₚ
this✝² : Module.Finite Rₚ Sₚ
this✝¹ : IsIntegrallyClosed Sₚ
this✝ : IsPrincipalIdealRing Rₚ
this : Module.Free Rₚ Sₚ
⊢ (trace (R ⧸ p) (S ⧸ pS)) ((Ideal.Quotient.mk pS) x) = (Ideal.Quotient.mk p) ((intTrace R S) x)

Tactic:
apply (equivQuotMaximalIdealOfIsLocalization p Rₚ).injective

Result:
case a
R : Type u_1
S : Type u_2
inst✝⁸ : CommRing R
inst✝⁷ : CommRing S
inst✝⁶ : Algebra R S
p : Ideal R
inst✝⁵ : p.IsMaximal
x : S
inst✝⁴ : IsDedekindDomain R
inst✝³ : IsDomain S
inst✝² : NoZeroSMulDivisors R S
inst✝¹ : Module.Finite R S
inst✝ : IsIntegrallyClosed S
Rₚ : Type u_1 := Localization.AtPrime p
Sₚ : Type u_2 := Localization (algebraMapSubmonoid S p.primeCompl)
this✝⁷ : Algebra Rₚ Sₚ := localizationAlgebra p.primeCompl S
this✝⁶ : IsScalarTower R Rₚ Sₚ
this✝⁵ : IsLocalization (Submonoid.map (algebraMap R S) p.primeCompl) Sₚ
e : algebraMapSubmonoid S p.primeCompl ≤ S⁰
this✝⁴ : IsDomain Sₚ
this✝³ : NoZeroSMulDivisors Rₚ Sₚ
this✝² : Module.Finite Rₚ Sₚ
this✝¹ : IsIntegrallyClosed Sₚ
this✝ : IsPrincipalIdealRing Rₚ
this : Module.Free Rₚ Sₚ
⊢ (equivQuotMaximalIdealOfIsLocalization p Rₚ) ((trace (R ⧸ p) (S ⧸ pS)) ((Ideal.Quotient.mk pS) x)) =
    (equivQuotMaximalIdealOfIsLocalization p Rₚ) ((Ideal.Quotient.mk p) ((intTrace R S) x))

Proof state:
case a
R : Type u_1
S : Type u_2
inst✝⁸ : CommRing R
inst✝⁷ : CommRing S
inst✝⁶ : Algebra R S
p : Ideal R
inst✝⁵ : p.IsMaximal
x : S
inst✝⁴ : IsDedekindDomain R
inst✝³ : IsDomain S
inst✝² : NoZeroSMulDivisors R S
inst✝¹ : Module.Finite R S
inst✝ : IsIntegrallyClosed S
Rₚ : Type u_1 := Localization.AtPrime p
Sₚ : Type u_2 := Localization (algebraMapSubmonoid S p.primeCompl)
this✝⁷ : Algebra Rₚ Sₚ := localizationAlgebra p.primeCompl S
this✝⁶ : IsScalarTower R Rₚ Sₚ
this✝⁵ : IsLocalization (Submonoid.map (algebraMap R S) p.primeCompl) Sₚ
e : algebraMapSubmonoid S p.primeCompl ≤ S⁰
this✝⁴ : IsDomain Sₚ
this✝³ : NoZeroSMulDivisors Rₚ Sₚ
this✝² : Module.Finite Rₚ Sₚ
this✝¹ : IsIntegrallyClosed Sₚ
this✝ : IsPrincipalIdealRing Rₚ
this : Module.Free Rₚ Sₚ
⊢ (algebraMap R (Rₚ ⧸ maximalIdeal Rₚ)) ((intTrace R S) x) =
    (equivQuotMaximalIdealOfIsLocalization p Rₚ) ((Ideal.Quotient.mk p) ((intTrace R S) x))

Tactic:
simp only [equivQuotMaximalIdealOfIsLocalization, RingHom.quotientKerEquivOfSurjective,
  RingEquiv.coe_trans, Function.comp_apply, Ideal.quotEquivOfEq_mk,
  RingHom.quotientKerEquivOfRightInverse.apply, RingHom.kerLift_mk]

Result:
no goals

Proof state:
R : Type u_1
S : Type u_2
inst✝⁸ : CommRing R
inst✝⁷ : CommRing S
inst✝⁶ : Algebra R S
p : Ideal R
inst✝⁵ : p.IsMaximal
x : S
inst✝⁴ : IsDedekindDomain R
inst✝³ : IsDomain S
inst✝² : NoZeroSMulDivisors R S
inst✝¹ : Module.Finite R S
inst✝ : IsIntegrallyClosed S
Rₚ : Type u_1 := Localization.AtPrime p
Sₚ : Type u_2 := Localization (algebraMapSubmonoid S p.primeCompl)
this✝² : Algebra Rₚ Sₚ := localizationAlgebra p.primeCompl S
this✝¹ : IsScalarTower R Rₚ Sₚ
this✝ : IsLocalization (Submonoid.map (algebraMap R S) p.primeCompl) Sₚ
e : algebraMapSubmonoid S p.primeCompl ≤ S⁰
this : IsDomain Sₚ
⊢ NoZeroSMulDivisors Rₚ Sₚ

Tactic:
rw [NoZeroSMulDivisors.iff_algebraMap_injective, RingHom.injective_iff_ker_eq_bot,
  RingHom.ker_eq_bot_iff_eq_zero]

Result:
R : Type u_1
S : Type u_2
inst✝⁸ : CommRing R
inst✝⁷ : CommRing S
inst✝⁶ : Algebra R S
p : Ideal R
inst✝⁵ : p.IsMaximal
x : S
inst✝⁴ : IsDedekindDomain R
inst✝³ : IsDomain S
inst✝² : NoZeroSMulDivisors R S
inst✝¹ : Module.Finite R S
inst✝ : IsIntegrallyClosed S
Rₚ : Type u_1 := Localization.AtPrime p
Sₚ : Type u_2 := Localization (algebraMapSubmonoid S p.primeCompl)
this✝² : Algebra Rₚ Sₚ := localizationAlgebra p.primeCompl S
this✝¹ : IsScalarTower R Rₚ Sₚ
this✝ : IsLocalization (Submonoid.map (algebraMap R S) p.primeCompl) Sₚ
e : algebraMapSubmonoid S p.primeCompl ≤ S⁰
this : IsDomain Sₚ
⊢ ∀ (x : Rₚ), (algebraMap Rₚ Sₚ) x = 0 → x = 0

Proof state:
case neg
R : Type u_1
S : Type u_2
inst✝⁸ : CommRing R
inst✝⁷ : CommRing S
inst✝⁶ : Algebra R S
p : Ideal R
inst✝⁵ : p.IsMaximal
x : S
inst✝⁴ : IsDedekindDomain R
inst✝³ : IsDomain S
inst✝² : NoZeroSMulDivisors R S
inst✝¹ : Module.Finite R S
inst✝ : IsIntegrallyClosed S
Rₚ : Type u_1 := Localization.AtPrime p
Sₚ : Type u_2 := Localization (algebraMapSubmonoid S p.primeCompl)
this✝⁶ : Algebra Rₚ Sₚ := localizationAlgebra p.primeCompl S
this✝⁵ : IsScalarTower R Rₚ Sₚ
this✝⁴ : IsLocalization (Submonoid.map (algebraMap R S) p.primeCompl) Sₚ
e : algebraMapSubmonoid S p.primeCompl ≤ S⁰
this✝³ : IsDomain Sₚ
this✝² : NoZeroSMulDivisors Rₚ Sₚ
this✝¹ : Module.Finite Rₚ Sₚ
this✝ : IsIntegrallyClosed Sₚ
hp : ¬p = ⊥
this : IsDiscreteValuationRing (Localization.AtPrime p)
⊢ IsPrincipalIdealRing Rₚ

Tactic:
infer_instance

Result:
no goals