-- Mathlib/NumberTheory/KummerDedekind.lean
theorem Ideal.irreducible_map_of_irreducible_minpoly (hI : IsMaximal I) (hI' : I ≠ ⊥)
    (hx : (conductor R x).comap (algebraMap R S) ⊔ I = ⊤) (hx' : IsIntegral R x)
    (hf : Irreducible (Polynomial.map (Ideal.Quotient.mk I) (minpoly R x))) :
    Irreducible (I.map (algebraMap R S))

Proof state:
case intro
R : Type u_1
S : Type u_2
inst✝⁶ : CommRing R
inst✝⁵ : CommRing S
inst✝⁴ : Algebra R S
x : S
I : Ideal R
inst✝³ : IsDomain R
inst✝² : IsIntegrallyClosed R
inst✝¹ : IsDedekindDomain S
inst✝ : NoZeroSMulDivisors R S
hI : I.IsMaximal
hI' : I ≠ ⊥
hx : comap (algebraMap R S) (conductor R x) ⊔ I = ⊤
hx' : _root_.IsIntegral R x
hf : Irreducible (Polynomial.map (Ideal.Quotient.mk I) (minpoly R x))
mem_norm_factors :
  normalize (Polynomial.map (Ideal.Quotient.mk I) (minpoly R x)) ∈
    normalizedFactors (Polynomial.map (Ideal.Quotient.mk I) (minpoly R x))
y : Ideal S
hy : normalizedFactors (Ideal.map (algebraMap R S) I) = {y}
⊢ Irreducible (Ideal.map (algebraMap R S) I)

Tactic:
have h := prod_normalizedFactors (show I.map (algebraMap R S) ≠ 0 by
      rwa [← bot_eq_zero, Ne,
        map_eq_bot_iff_of_injective (FaithfulSMul.algebraMap_injective R S)])

Result:
case intro
R : Type u_1
S : Type u_2
inst✝⁶ : CommRing R
inst✝⁵ : CommRing S
inst✝⁴ : Algebra R S
x : S
I : Ideal R
inst✝³ : IsDomain R
inst✝² : IsIntegrallyClosed R
inst✝¹ : IsDedekindDomain S
inst✝ : NoZeroSMulDivisors R S
hI : I.IsMaximal
hI' : I ≠ ⊥
hx : comap (algebraMap R S) (conductor R x) ⊔ I = ⊤
hx' : _root_.IsIntegral R x
hf : Irreducible (Polynomial.map (Ideal.Quotient.mk I) (minpoly R x))
mem_norm_factors :
  normalize (Polynomial.map (Ideal.Quotient.mk I) (minpoly R x)) ∈
    normalizedFactors (Polynomial.map (Ideal.Quotient.mk I) (minpoly R x))
y : Ideal S
hy : normalizedFactors (Ideal.map (algebraMap R S) I) = {y}
h : Associated (normalizedFactors (Ideal.map (algebraMap R S) I)).prod (Ideal.map (algebraMap R S) I)
⊢ Irreducible (Ideal.map (algebraMap R S) I)

Proof state:
case h
R : Type u_1
S : Type u_2
inst✝⁶ : CommRing R
inst✝⁵ : CommRing S
inst✝⁴ : Algebra R S
x : S
I : Ideal R
inst✝³ : IsDomain R
inst✝² : IsIntegrallyClosed R
inst✝¹ : IsDedekindDomain S
inst✝ : NoZeroSMulDivisors R S
hI : I.IsMaximal
hI' : I ≠ ⊥
hx : comap (algebraMap R S) (conductor R x) ⊔ I = ⊤
hx' : _root_.IsIntegral R x
hf : Irreducible (Polynomial.map (Ideal.Quotient.mk I) (minpoly R x))
mem_norm_factors :
  normalize (Polynomial.map (Ideal.Quotient.mk I) (minpoly R x)) ∈
    normalizedFactors (Polynomial.map (Ideal.Quotient.mk I) (minpoly R x))
⊢ (normalizedFactors (Polynomial.map (Ideal.Quotient.mk I) (minpoly R x))).attach =
    {⟨normalize (Polynomial.map (Ideal.Quotient.mk I) (minpoly R x)), mem_norm_factors⟩}

Tactic:
apply Multiset.map_injective Subtype.coe_injective

Result:
case h.a
R : Type u_1
S : Type u_2
inst✝⁶ : CommRing R
inst✝⁵ : CommRing S
inst✝⁴ : Algebra R S
x : S
I : Ideal R
inst✝³ : IsDomain R
inst✝² : IsIntegrallyClosed R
inst✝¹ : IsDedekindDomain S
inst✝ : NoZeroSMulDivisors R S
hI : I.IsMaximal
hI' : I ≠ ⊥
hx : comap (algebraMap R S) (conductor R x) ⊔ I = ⊤
hx' : _root_.IsIntegral R x
hf : Irreducible (Polynomial.map (Ideal.Quotient.mk I) (minpoly R x))
mem_norm_factors :
  normalize (Polynomial.map (Ideal.Quotient.mk I) (minpoly R x)) ∈
    normalizedFactors (Polynomial.map (Ideal.Quotient.mk I) (minpoly R x))
⊢ Multiset.map (fun a => ↑a) (normalizedFactors (Polynomial.map (Ideal.Quotient.mk I) (minpoly R x))).attach =
    Multiset.map (fun a => ↑a) {⟨normalize (Polynomial.map (Ideal.Quotient.mk I) (minpoly R x)), mem_norm_factors⟩}

Proof state:
R : Type u_1
S : Type u_2
inst✝⁶ : CommRing R
inst✝⁵ : CommRing S
inst✝⁴ : Algebra R S
x : S
I : Ideal R
inst✝³ : IsDomain R
inst✝² : IsIntegrallyClosed R
inst✝¹ : IsDedekindDomain S
inst✝ : NoZeroSMulDivisors R S
hI : I.IsMaximal
hI' : I ≠ ⊥
hx : comap (algebraMap R S) (conductor R x) ⊔ I = ⊤
hx' : _root_.IsIntegral R x
hf : Irreducible (Polynomial.map (Ideal.Quotient.mk I) (minpoly R x))
⊢ normalize (Polynomial.map (Ideal.Quotient.mk I) (minpoly R x)) ∈
    normalizedFactors (Polynomial.map (Ideal.Quotient.mk I) (minpoly R x))

Tactic:
simp [normalizedFactors_irreducible hf]

Result:
no goals

Proof state:
R : Type u_1
S : Type u_2
inst✝⁶ : CommRing R
inst✝⁵ : CommRing S
inst✝⁴ : Algebra R S
x : S
I : Ideal R
inst✝³ : IsDomain R
inst✝² : IsIntegrallyClosed R
inst✝¹ : IsDedekindDomain S
inst✝ : NoZeroSMulDivisors R S
hI : I.IsMaximal
hI' : I ≠ ⊥
hx : comap (algebraMap R S) (conductor R x) ⊔ I = ⊤
hx' : _root_.IsIntegral R x
hf : Irreducible (Polynomial.map (Ideal.Quotient.mk I) (minpoly R x))
mem_norm_factors :
  normalize (Polynomial.map (Ideal.Quotient.mk I) (minpoly R x)) ∈
    normalizedFactors (Polynomial.map (Ideal.Quotient.mk I) (minpoly R x))
this : ∃ y, normalizedFactors (Ideal.map (algebraMap R S) I) = {y}
⊢ Irreducible (Ideal.map (algebraMap R S) I)

Tactic:
obtain ⟨y, hy⟩ := this

Result:
case intro
R : Type u_1
S : Type u_2
inst✝⁶ : CommRing R
inst✝⁵ : CommRing S
inst✝⁴ : Algebra R S
x : S
I : Ideal R
inst✝³ : IsDomain R
inst✝² : IsIntegrallyClosed R
inst✝¹ : IsDedekindDomain S
inst✝ : NoZeroSMulDivisors R S
hI : I.IsMaximal
hI' : I ≠ ⊥
hx : comap (algebraMap R S) (conductor R x) ⊔ I = ⊤
hx' : _root_.IsIntegral R x
hf : Irreducible (Polynomial.map (Ideal.Quotient.mk I) (minpoly R x))
mem_norm_factors :
  normalize (Polynomial.map (Ideal.Quotient.mk I) (minpoly R x)) ∈
    normalizedFactors (Polynomial.map (Ideal.Quotient.mk I) (minpoly R x))
y : Ideal S
hy : normalizedFactors (Ideal.map (algebraMap R S) I) = {y}
⊢ Irreducible (Ideal.map (algebraMap R S) I)

Proof state:
case intro
R : Type u_1
S : Type u_2
inst✝⁶ : CommRing R
inst✝⁵ : CommRing S
inst✝⁴ : Algebra R S
x : S
I : Ideal R
inst✝³ : IsDomain R
inst✝² : IsIntegrallyClosed R
inst✝¹ : IsDedekindDomain S
inst✝ : NoZeroSMulDivisors R S
hI : I.IsMaximal
hI' : I ≠ ⊥
hx : comap (algebraMap R S) (conductor R x) ⊔ I = ⊤
hx' : _root_.IsIntegral R x
hf : Irreducible (Polynomial.map (Ideal.Quotient.mk I) (minpoly R x))
mem_norm_factors :
  normalize (Polynomial.map (Ideal.Quotient.mk I) (minpoly R x)) ∈
    normalizedFactors (Polynomial.map (Ideal.Quotient.mk I) (minpoly R x))
y : Ideal S
hy : normalizedFactors (Ideal.map (algebraMap R S) I) = {y}
h : y = Ideal.map (algebraMap R S) I
⊢ Irreducible (Ideal.map (algebraMap R S) I)

Tactic:
rw [← h]

Result:
case intro
R : Type u_1
S : Type u_2
inst✝⁶ : CommRing R
inst✝⁵ : CommRing S
inst✝⁴ : Algebra R S
x : S
I : Ideal R
inst✝³ : IsDomain R
inst✝² : IsIntegrallyClosed R
inst✝¹ : IsDedekindDomain S
inst✝ : NoZeroSMulDivisors R S
hI : I.IsMaximal
hI' : I ≠ ⊥
hx : comap (algebraMap R S) (conductor R x) ⊔ I = ⊤
hx' : _root_.IsIntegral R x
hf : Irreducible (Polynomial.map (Ideal.Quotient.mk I) (minpoly R x))
mem_norm_factors :
  normalize (Polynomial.map (Ideal.Quotient.mk I) (minpoly R x)) ∈
    normalizedFactors (Polynomial.map (Ideal.Quotient.mk I) (minpoly R x))
y : Ideal S
hy : normalizedFactors (Ideal.map (algebraMap R S) I) = {y}
h : y = Ideal.map (algebraMap R S) I
⊢ Irreducible y