-- Mathlib/RingTheory/Jacobson/Ring.lean
private lemma aux_IH {R : Type u} {S : Type v} {T : Type w}
  [CommRing R] [CommRing S] [CommRing T] [IsJacobsonRing S] [Algebra R S] [Algebra R T]
  (IH : ∀ (Q : Ideal S), (IsMaximal Q) → RingHom.IsIntegral (algebraMap R (S ⧸ Q)))
  (v : S[X] ≃ₐ[R] T) (P : Ideal T) (hP : P.IsMaximal) :
  RingHom.IsIntegral (algebraMap R (T ⧸ P))

Proof state:
R : Type u
S : Type v
T : Type w
inst✝⁵ : CommRing R
inst✝⁴ : CommRing S
inst✝³ : CommRing T
inst✝² : IsJacobsonRing S
inst✝¹ : Algebra R S
inst✝ : Algebra R T
IH : ∀ (Q : Ideal S), Q.IsMaximal → (algebraMap R (S ⧸ Q)).IsIntegral
v : S[X] ≃ₐ[R] T
P : Ideal T
hP : P.IsMaximal
Q : Ideal S[X] := comap (↑v).toRingHom P
⊢ (algebraMap R (T ⧸ P)).IsIntegral

Tactic:
have hw : Ideal.map v Q = P := map_comap_of_surjective v v.surjective P

Result:
R : Type u
S : Type v
T : Type w
inst✝⁵ : CommRing R
inst✝⁴ : CommRing S
inst✝³ : CommRing T
inst✝² : IsJacobsonRing S
inst✝¹ : Algebra R S
inst✝ : Algebra R T
IH : ∀ (Q : Ideal S), Q.IsMaximal → (algebraMap R (S ⧸ Q)).IsIntegral
v : S[X] ≃ₐ[R] T
P : Ideal T
hP : P.IsMaximal
Q : Ideal S[X] := comap (↑v).toRingHom P
hw : Ideal.map v Q = P
⊢ (algebraMap R (T ⧸ P)).IsIntegral

Proof state:
case hg
R : Type u
S : Type v
T : Type w
inst✝⁵ : CommRing R
inst✝⁴ : CommRing S
inst✝³ : CommRing T
inst✝² : IsJacobsonRing S
inst✝¹ : Algebra R S
inst✝ : Algebra R T
IH : ∀ (Q : Ideal S), Q.IsMaximal → (algebraMap R (S ⧸ Q)).IsIntegral
v : S[X] ≃ₐ[R] T
P : Ideal T
hP : P.IsMaximal
Q : Ideal S[X] := comap (↑v).toRingHom P
hw : Ideal.map v Q = P
hQ : Q.IsMaximal
w : (S[X] ⧸ Q) ≃ₐ[R] T ⧸ P := Q.quotientEquivAlg P v ⋯
Q' : Ideal S := comap Polynomial.C Q
w' : S ⧸ Q' →ₐ[R] S[X] ⧸ Q := quotientMapₐ Q (MvPolynomial.Cₐ R S) ⋯
h_eq : algebraMap R (T ⧸ P) = w.toRingEquiv.toRingHom.comp (w'.comp (algebraMap R (S ⧸ Q')))
⊢ w.toRingEquiv.toRingHom.IsIntegral

Tactic:
apply RingHom.isIntegral_of_surjective

Result:
case hg.hf
R : Type u
S : Type v
T : Type w
inst✝⁵ : CommRing R
inst✝⁴ : CommRing S
inst✝³ : CommRing T
inst✝² : IsJacobsonRing S
inst✝¹ : Algebra R S
inst✝ : Algebra R T
IH : ∀ (Q : Ideal S), Q.IsMaximal → (algebraMap R (S ⧸ Q)).IsIntegral
v : S[X] ≃ₐ[R] T
P : Ideal T
hP : P.IsMaximal
Q : Ideal S[X] := comap (↑v).toRingHom P
hw : Ideal.map v Q = P
hQ : Q.IsMaximal
w : (S[X] ⧸ Q) ≃ₐ[R] T ⧸ P := Q.quotientEquivAlg P v ⋯
Q' : Ideal S := comap Polynomial.C Q
w' : S ⧸ Q' →ₐ[R] S[X] ⧸ Q := quotientMapₐ Q (MvPolynomial.Cₐ R S) ⋯
h_eq : algebraMap R (T ⧸ P) = w.toRingEquiv.toRingHom.comp (w'.comp (algebraMap R (S ⧸ Q')))
⊢ Function.Surjective ⇑w.toRingEquiv.toRingHom

Proof state:
R : Type u
S : Type v
T : Type w
inst✝⁵ : CommRing R
inst✝⁴ : CommRing S
inst✝³ : CommRing T
inst✝² : IsJacobsonRing S
inst✝¹ : Algebra R S
inst✝ : Algebra R T
IH : ∀ (Q : Ideal S), Q.IsMaximal → (algebraMap R (S ⧸ Q)).IsIntegral
v : S[X] ≃ₐ[R] T
P : Ideal T
hP : P.IsMaximal
Q : Ideal S[X] := comap (↑v).toRingHom P
hw : Ideal.map v Q = P
hQ : Q.IsMaximal
w : (S[X] ⧸ Q) ≃ₐ[R] T ⧸ P := Q.quotientEquivAlg P v ⋯
Q' : Ideal S := comap Polynomial.C Q
w' : S ⧸ Q' →ₐ[R] S[X] ⧸ Q := quotientMapₐ Q (MvPolynomial.Cₐ R S) ⋯
h_eq : algebraMap R (T ⧸ P) = w.toRingEquiv.toRingHom.comp (w'.comp (algebraMap R (S ⧸ Q')))
this : w'.toRingHom = quotientMap Q Polynomial.C ⋯
⊢ w'.IsIntegral

Tactic:
rw [this]

Result:
R : Type u
S : Type v
T : Type w
inst✝⁵ : CommRing R
inst✝⁴ : CommRing S
inst✝³ : CommRing T
inst✝² : IsJacobsonRing S
inst✝¹ : Algebra R S
inst✝ : Algebra R T
IH : ∀ (Q : Ideal S), Q.IsMaximal → (algebraMap R (S ⧸ Q)).IsIntegral
v : S[X] ≃ₐ[R] T
P : Ideal T
hP : P.IsMaximal
Q : Ideal S[X] := comap (↑v).toRingHom P
hw : Ideal.map v Q = P
hQ : Q.IsMaximal
w : (S[X] ⧸ Q) ≃ₐ[R] T ⧸ P := Q.quotientEquivAlg P v ⋯
Q' : Ideal S := comap Polynomial.C Q
w' : S ⧸ Q' →ₐ[R] S[X] ⧸ Q := quotientMapₐ Q (MvPolynomial.Cₐ R S) ⋯
h_eq : algebraMap R (T ⧸ P) = w.toRingEquiv.toRingHom.comp (w'.comp (algebraMap R (S ⧸ Q')))
this : w'.toRingHom = quotientMap Q Polynomial.C ⋯
⊢ (quotientMap Q Polynomial.C ⋯).IsIntegral

Proof state:
case hf.hf.a
R : Type u
S : Type v
T : Type w
inst✝⁵ : CommRing R
inst✝⁴ : CommRing S
inst✝³ : CommRing T
inst✝² : IsJacobsonRing S
inst✝¹ : Algebra R S
inst✝ : Algebra R T
IH : ∀ (Q : Ideal S), Q.IsMaximal → (algebraMap R (S ⧸ Q)).IsIntegral
v : S[X] ≃ₐ[R] T
P : Ideal T
hP : P.IsMaximal
Q : Ideal S[X] := comap (↑v).toRingHom P
hw : Ideal.map v Q = P
hQ : Q.IsMaximal
w : (S[X] ⧸ Q) ≃ₐ[R] T ⧸ P := Q.quotientEquivAlg P v ⋯
Q' : Ideal S := comap Polynomial.C Q
w' : S ⧸ Q' →ₐ[R] S[X] ⧸ Q := quotientMapₐ Q (MvPolynomial.Cₐ R S) ⋯
h_eq : algebraMap R (T ⧸ P) = w.toRingEquiv.toRingHom.comp (w'.comp (algebraMap R (S ⧸ Q')))
⊢ Q'.IsMaximal

Tactic:
apply Polynomial.isMaximal_comap_C_of_isJacobsonRing

Result:
no goals

Proof state:
case a
R : Type u
S : Type v
T : Type w
inst✝⁵ : CommRing R
inst✝⁴ : CommRing S
inst✝³ : CommRing T
inst✝² : IsJacobsonRing S
inst✝¹ : Algebra R S
inst✝ : Algebra R T
IH : ∀ (Q : Ideal S), Q.IsMaximal → (algebraMap R (S ⧸ Q)).IsIntegral
v : S[X] ≃ₐ[R] T
P : Ideal T
hP : P.IsMaximal
Q : Ideal S[X] := comap (↑v).toRingHom P
hw : Ideal.map v Q = P
hQ : Q.IsMaximal
w : (S[X] ⧸ Q) ≃ₐ[R] T ⧸ P := Q.quotientEquivAlg P v ⋯
Q' : Ideal S := comap Polynomial.C Q
w' : S ⧸ Q' →ₐ[R] S[X] ⧸ Q := quotientMapₐ Q (MvPolynomial.Cₐ R S) ⋯
r : R
⊢ (algebraMap R (T ⧸ P)) r = (w.toRingEquiv.toRingHom.comp (w'.comp (algebraMap R (S ⧸ Q')))) r

Tactic:
simp only [AlgEquiv.toAlgHom_eq_coe, AlgHom.toRingHom_eq_coe, AlgEquiv.toRingEquiv_eq_coe,
  RingEquiv.toRingHom_eq_coe, AlgHom.comp_algebraMap_of_tower, coe_comp, coe_coe,
  AlgEquiv.coe_ringEquiv, Function.comp_apply, AlgEquiv.commutes]

Result:
no goals

Proof state:
R : Type u
S : Type v
T : Type w
inst✝⁵ : CommRing R
inst✝⁴ : CommRing S
inst✝³ : CommRing T
inst✝² : IsJacobsonRing S
inst✝¹ : Algebra R S
inst✝ : Algebra R T
IH : ∀ (Q : Ideal S), Q.IsMaximal → (algebraMap R (S ⧸ Q)).IsIntegral
v : S[X] ≃ₐ[R] T
P : Ideal T
hP : P.IsMaximal
Q : Ideal S[X] := comap (↑v).toRingHom P
hw : Ideal.map v Q = P
hQ : Q.IsMaximal
w : (S[X] ⧸ Q) ≃ₐ[R] T ⧸ P := Q.quotientEquivAlg P v ⋯
Q' : Ideal S := comap Polynomial.C Q
⊢ (algebraMap R (T ⧸ P)).IsIntegral

Tactic:
let w' : (S ⧸ Q') →ₐ[R] (S[X] ⧸ Q) := Ideal.quotientMapₐ Q (Cₐ R S) le_rfl

Result:
R : Type u
S : Type v
T : Type w
inst✝⁵ : CommRing R
inst✝⁴ : CommRing S
inst✝³ : CommRing T
inst✝² : IsJacobsonRing S
inst✝¹ : Algebra R S
inst✝ : Algebra R T
IH : ∀ (Q : Ideal S), Q.IsMaximal → (algebraMap R (S ⧸ Q)).IsIntegral
v : S[X] ≃ₐ[R] T
P : Ideal T
hP : P.IsMaximal
Q : Ideal S[X] := comap (↑v).toRingHom P
hw : Ideal.map v Q = P
hQ : Q.IsMaximal
w : (S[X] ⧸ Q) ≃ₐ[R] T ⧸ P := Q.quotientEquivAlg P v ⋯
Q' : Ideal S := comap Polynomial.C Q
w' : S ⧸ Q' →ₐ[R] S[X] ⧸ Q := quotientMapₐ Q (MvPolynomial.Cₐ R S) ⋯
⊢ (algebraMap R (T ⧸ P)).IsIntegral

Proof state:
case hf.hg
R : Type u
S : Type v
T : Type w
inst✝⁵ : CommRing R
inst✝⁴ : CommRing S
inst✝³ : CommRing T
inst✝² : IsJacobsonRing S
inst✝¹ : Algebra R S
inst✝ : Algebra R T
IH : ∀ (Q : Ideal S), Q.IsMaximal → (algebraMap R (S ⧸ Q)).IsIntegral
v : S[X] ≃ₐ[R] T
P : Ideal T
hP : P.IsMaximal
Q : Ideal S[X] := comap (↑v).toRingHom P
hw : Ideal.map v Q = P
hQ : Q.IsMaximal
w : (S[X] ⧸ Q) ≃ₐ[R] T ⧸ P := Q.quotientEquivAlg P v ⋯
Q' : Ideal S := comap Polynomial.C Q
w' : S ⧸ Q' →ₐ[R] S[X] ⧸ Q := quotientMapₐ Q (MvPolynomial.Cₐ R S) ⋯
h_eq : algebraMap R (T ⧸ P) = w.toRingEquiv.toRingHom.comp (w'.comp (algebraMap R (S ⧸ Q')))
⊢ w'.toRingHom = quotientMap Q Polynomial.C ⋯

Tactic:
rfl

Result:
no goals