-- Mathlib/RingTheory/DedekindDomain/Different.lean
lemma conductor_mul_differentIdeal [NoZeroSMulDivisors A B]
    (x : B) (hx : Algebra.adjoin K {algebraMap B L x} = ⊤) :
    (conductor A x) * differentIdeal A B = Ideal.span {aeval x (derivative (minpoly A x))}

Proof state:
case a.a.h
A : Type u_1
K : Type u_2
L : Type u
B : Type u_3
inst✝¹⁸ : CommRing A
inst✝¹⁷ : Field K
inst✝¹⁶ : CommRing B
inst✝¹⁵ : Field L
inst✝¹⁴ : Algebra A K
inst✝¹³ : Algebra B L
inst✝¹² : Algebra A B
inst✝¹¹ : Algebra K L
inst✝¹⁰ : Algebra A L
inst✝⁹ : IsScalarTower A K L
inst✝⁸ : IsScalarTower A B L
inst✝⁷ : IsDomain A
inst✝⁶ : IsFractionRing A K
inst✝⁵ : FiniteDimensional K L
inst✝⁴ : Algebra.IsSeparable K L
inst✝³ : IsIntegralClosure B A L
inst✝² : IsIntegrallyClosed A
inst✝¹ : IsDedekindDomain B
inst✝ : NoZeroSMulDivisors A B
x : B
hx : adjoin K {(algebraMap B L) x} = ⊤
hAx : IsIntegral A x
this✝¹ : IsFractionRing B L
y : L
hne₁ : (aeval ((algebraMap B L) x)) (derivative (minpoly K ((algebraMap B L) x))) ≠ 0
this✝ : (algebraMap B L) ((aeval x) (derivative (minpoly A x))) ≠ 0
hne₂ : ((aeval ((algebraMap B L) x)) (derivative (minpoly K ((algebraMap B L) x))))⁻¹ ≠ 0
this : IsIntegral A ((algebraMap B L) x)
⊢ (∀ (z : B),
      ((aeval ((algebraMap B L) x)) (derivative (minpoly K ((algebraMap B L) x))))⁻¹ * (y * (algebraMap B L) z) ∈
        ((aeval ((algebraMap B L) x)) (derivative (minpoly K ((algebraMap B L) x))))⁻¹ •
          Subalgebra.toSubmodule (adjoin A {(algebraMap B L) x})) ↔
    ∀ a ∈ 1,
      ((traceForm K L) (((algebraMap B L) ((aeval x) (derivative (minpoly A x))))⁻¹ * y)) a ∈ (algebraMap A K).range

Tactic:
rw [← traceForm_dualSubmodule_adjoin A K hx this]

Result:
case a.a.h
A : Type u_1
K : Type u_2
L : Type u
B : Type u_3
inst✝¹⁸ : CommRing A
inst✝¹⁷ : Field K
inst✝¹⁶ : CommRing B
inst✝¹⁵ : Field L
inst✝¹⁴ : Algebra A K
inst✝¹³ : Algebra B L
inst✝¹² : Algebra A B
inst✝¹¹ : Algebra K L
inst✝¹⁰ : Algebra A L
inst✝⁹ : IsScalarTower A K L
inst✝⁸ : IsScalarTower A B L
inst✝⁷ : IsDomain A
inst✝⁶ : IsFractionRing A K
inst✝⁵ : FiniteDimensional K L
inst✝⁴ : Algebra.IsSeparable K L
inst✝³ : IsIntegralClosure B A L
inst✝² : IsIntegrallyClosed A
inst✝¹ : IsDedekindDomain B
inst✝ : NoZeroSMulDivisors A B
x : B
hx : adjoin K {(algebraMap B L) x} = ⊤
hAx : IsIntegral A x
this✝¹ : IsFractionRing B L
y : L
hne₁ : (aeval ((algebraMap B L) x)) (derivative (minpoly K ((algebraMap B L) x))) ≠ 0
this✝ : (algebraMap B L) ((aeval x) (derivative (minpoly A x))) ≠ 0
hne₂ : ((aeval ((algebraMap B L) x)) (derivative (minpoly K ((algebraMap B L) x))))⁻¹ ≠ 0
this : IsIntegral A ((algebraMap B L) x)
⊢ (∀ (z : B),
      ((aeval ((algebraMap B L) x)) (derivative (minpoly K ((algebraMap B L) x))))⁻¹ * (y * (algebraMap B L) z) ∈
        (traceForm K L).dualSubmodule (Subalgebra.toSubmodule (adjoin A {(algebraMap B L) x}))) ↔
    ∀ a ∈ 1,
      ((traceForm K L) (((algebraMap B L) ((aeval x) (derivative (minpoly A x))))⁻¹ * y)) a ∈ (algebraMap A K).range

Proof state:
case a.a.h
A : Type u_1
K : Type u_2
L : Type u
B : Type u_3
inst✝¹⁸ : CommRing A
inst✝¹⁷ : Field K
inst✝¹⁶ : CommRing B
inst✝¹⁵ : Field L
inst✝¹⁴ : Algebra A K
inst✝¹³ : Algebra B L
inst✝¹² : Algebra A B
inst✝¹¹ : Algebra K L
inst✝¹⁰ : Algebra A L
inst✝⁹ : IsScalarTower A K L
inst✝⁸ : IsScalarTower A B L
inst✝⁷ : IsDomain A
inst✝⁶ : IsFractionRing A K
inst✝⁵ : FiniteDimensional K L
inst✝⁴ : Algebra.IsSeparable K L
inst✝³ : IsIntegralClosure B A L
inst✝² : IsIntegrallyClosed A
inst✝¹ : IsDedekindDomain B
inst✝ : NoZeroSMulDivisors A B
x : B
hx : adjoin K {(algebraMap B L) x} = ⊤
hAx : IsIntegral A x
this✝¹ : IsFractionRing B L
y : L
hne₁ : (aeval ((algebraMap B L) x)) (derivative (minpoly K ((algebraMap B L) x))) ≠ 0
this✝ : (algebraMap B L) ((aeval x) (derivative (minpoly A x))) ≠ 0
hne₂ : ((aeval ((algebraMap B L) x)) (derivative (minpoly K ((algebraMap B L) x))))⁻¹ ≠ 0
this : IsIntegral A ((algebraMap B L) x)
⊢ (∀ (z : B),
      ((aeval ((algebraMap B L) x)) (derivative (minpoly K ((algebraMap B L) x))))⁻¹ * (y * (algebraMap B L) z) ∈
        (traceForm K L).dualSubmodule (Subalgebra.toSubmodule (adjoin A {(algebraMap B L) x}))) ↔
    ∀ a ∈ 1,
      ((traceForm K L) (((algebraMap B L) ((aeval x) (derivative (minpoly A x))))⁻¹ * y)) a ∈ (algebraMap A K).range

Tactic:
simp only [LinearMap.BilinForm.mem_dualSubmodule, traceForm_apply, Subalgebra.mem_toSubmodule,
  minpoly.isIntegrallyClosed_eq_field_fractions K L hAx,
  derivative_map, aeval_map_algebraMap, aeval_algebraMap_apply, mul_assoc,
  FractionalIdeal.mem_one_iff, forall_exists_index, forall_apply_eq_imp_iff]

Result:
case a.a.h
A : Type u_1
K : Type u_2
L : Type u
B : Type u_3
inst✝¹⁸ : CommRing A
inst✝¹⁷ : Field K
inst✝¹⁶ : CommRing B
inst✝¹⁵ : Field L
inst✝¹⁴ : Algebra A K
inst✝¹³ : Algebra B L
inst✝¹² : Algebra A B
inst✝¹¹ : Algebra K L
inst✝¹⁰ : Algebra A L
inst✝⁹ : IsScalarTower A K L
inst✝⁸ : IsScalarTower A B L
inst✝⁷ : IsDomain A
inst✝⁶ : IsFractionRing A K
inst✝⁵ : FiniteDimensional K L
inst✝⁴ : Algebra.IsSeparable K L
inst✝³ : IsIntegralClosure B A L
inst✝² : IsIntegrallyClosed A
inst✝¹ : IsDedekindDomain B
inst✝ : NoZeroSMulDivisors A B
x : B
hx : adjoin K {(algebraMap B L) x} = ⊤
hAx : IsIntegral A x
this✝¹ : IsFractionRing B L
y : L
hne₁ : (aeval ((algebraMap B L) x)) (derivative (minpoly K ((algebraMap B L) x))) ≠ 0
this✝ : (algebraMap B L) ((aeval x) (derivative (minpoly A x))) ≠ 0
hne₂ : ((aeval ((algebraMap B L) x)) (derivative (minpoly K ((algebraMap B L) x))))⁻¹ ≠ 0
this : IsIntegral A ((algebraMap B L) x)
⊢ (∀ (z : B),
      ∀ y_1 ∈ adjoin A {(algebraMap B L) x},
        (Algebra.trace K L)
            (((algebraMap B L) ((aeval x) (derivative (minpoly A x))))⁻¹ * (y * ((algebraMap B L) z * y_1))) ∈
          1) ↔
    ∀ (a : B),
      (Algebra.trace K L) (((algebraMap B L) ((aeval x) (derivative (minpoly A x))))⁻¹ * (y * (algebraMap B L) a)) ∈
        (algebraMap A K).range

Proof state:
case a.a.h
A : Type u_1
K : Type u_2
L : Type u
B : Type u_3
inst✝¹⁸ : CommRing A
inst✝¹⁷ : Field K
inst✝¹⁶ : CommRing B
inst✝¹⁵ : Field L
inst✝¹⁴ : Algebra A K
inst✝¹³ : Algebra B L
inst✝¹² : Algebra A B
inst✝¹¹ : Algebra K L
inst✝¹⁰ : Algebra A L
inst✝⁹ : IsScalarTower A K L
inst✝⁸ : IsScalarTower A B L
inst✝⁷ : IsDomain A
inst✝⁶ : IsFractionRing A K
inst✝⁵ : FiniteDimensional K L
inst✝⁴ : Algebra.IsSeparable K L
inst✝³ : IsIntegralClosure B A L
inst✝² : IsIntegrallyClosed A
inst✝¹ : IsDedekindDomain B
inst✝ : NoZeroSMulDivisors A B
x : B
hx : adjoin K {(algebraMap B L) x} = ⊤
hAx : IsIntegral A x
this : IsFractionRing B L
y : L
⊢ y ∈ coeSubmodule L (conductor A x) ↔
    y ∈ (algebraMap B L) ((aeval x) (derivative (minpoly A x))) • ↑(FractionalIdeal.dual A K 1)

Tactic:
have hne₁ : aeval (algebraMap B L x) (derivative (minpoly K (algebraMap B L x))) ≠ 0 :=
  (Algebra.IsSeparable.isSeparable _ _).aeval_derivative_ne_zero (minpoly.aeval _ _)

Result:
case a.a.h
A : Type u_1
K : Type u_2
L : Type u
B : Type u_3
inst✝¹⁸ : CommRing A
inst✝¹⁷ : Field K
inst✝¹⁶ : CommRing B
inst✝¹⁵ : Field L
inst✝¹⁴ : Algebra A K
inst✝¹³ : Algebra B L
inst✝¹² : Algebra A B
inst✝¹¹ : Algebra K L
inst✝¹⁰ : Algebra A L
inst✝⁹ : IsScalarTower A K L
inst✝⁸ : IsScalarTower A B L
inst✝⁷ : IsDomain A
inst✝⁶ : IsFractionRing A K
inst✝⁵ : FiniteDimensional K L
inst✝⁴ : Algebra.IsSeparable K L
inst✝³ : IsIntegralClosure B A L
inst✝² : IsIntegrallyClosed A
inst✝¹ : IsDedekindDomain B
inst✝ : NoZeroSMulDivisors A B
x : B
hx : adjoin K {(algebraMap B L) x} = ⊤
hAx : IsIntegral A x
this : IsFractionRing B L
y : L
hne₁ : (aeval ((algebraMap B L) x)) (derivative (minpoly K ((algebraMap B L) x))) ≠ 0
⊢ y ∈ coeSubmodule L (conductor A x) ↔
    y ∈ (algebraMap B L) ((aeval x) (derivative (minpoly A x))) • ↑(FractionalIdeal.dual A K 1)