-- Mathlib/RingTheory/RingHom/Integral.lean
theorem isIntegral_ofLocalizationSpan :
    OfLocalizationSpan (RingHom.IsIntegral ·)

Proof state:
case pos
R S : Type u_1
inst✝¹ : CommRing R
inst✝ : CommRing S
f : R →+* S
s : Set R
hs : Ideal.span s = ⊤
H : ∀ (r : ↑s), (fun {R S} [CommRing R] [CommRing S] x => x.IsIntegral) (Localization.awayMap f ↑r)
r : S
this✝³ : Algebra R S := f.toAlgebra
t : R
ht : t ∈ s
this✝² : Algebra (Localization.Away t) (Localization.Away (f t)) := (Localization.awayMap f t).toAlgebra
this✝¹ : IsScalarTower R (Localization.Away t) (Localization.Away (f t))
this✝ : _root_.IsIntegral (Localization.Away t) ((algebraMap S (Localization.Away (f t))) r)
n : ℕ
p : R[X]
hp : p.Monic
m : ℕ
hp' : 1 ≤ p.natDegree
e : t ^ m • eval₂ (algebraMap R S) (t ^ n • r) p = 0
this :
  eval₂ (algebraMap R S) (t ^ m • t ^ n • r) (p.scaleRoots (t ^ m)) =
    (t ^ m) ^ p.natDegree • eval₂ (algebraMap R S) (t ^ n • r) p
⊢ eval₂ (algebraMap R S) (t ^ m • t ^ n • r) (p.scaleRoots (t ^ m)) = 0

Tactic:
rw [this, ← tsub_add_cancel_of_le hp', pow_succ, mul_smul, e, smul_zero]

Result:
no goals

Proof state:
⊢ OfLocalizationSpan fun {R S} [CommRing R] [CommRing S] x => x.IsIntegral

Tactic:
introv R hs H r

Result:
R S : Type u_1
inst✝¹ : CommRing R
inst✝ : CommRing S
f : R →+* S
s : Set R
hs : Ideal.span s = ⊤
H : ∀ (r : ↑s), (fun {R S} [CommRing R] [CommRing S] x => x.IsIntegral) (Localization.awayMap f ↑r)
r : S
⊢ f.IsIntegralElem r

Proof state:
R S : Type u_1
inst✝¹ : CommRing R
inst✝ : CommRing S
f : R →+* S
s : Set R
hs : Ideal.span s = ⊤
H : ∀ (r : ↑s), (fun {R S} [CommRing R] [CommRing S] x => x.IsIntegral) (Localization.awayMap f ↑r)
r : S
this✝² : Algebra R S := f.toAlgebra
t : R
ht : t ∈ s
this✝¹ : Algebra (Localization.Away t) (Localization.Away (f t)) := (Localization.awayMap f t).toAlgebra
this✝ : IsScalarTower R (Localization.Away t) (Localization.Away (f t))
this : _root_.IsIntegral (Localization.Away t) ((algebraMap S (Localization.Away (f t))) r)
n m : ℕ
hp : Monic 1
e : ↑⟨(algebraMap R S) t ^ m, ⋯⟩ * eval₂ (algebraMap R S) ((algebraMap R S) ↑⟨(fun x => t ^ x) n, ⋯⟩ * r) 1 = 0
hp' : ¬1 ≤ natDegree 1
⊢ ↑⟨t, ht⟩ ^ m • r ∈ Subalgebra.toSubmodule (integralClosure R S)

Tactic:
simp [Algebra.smul_def, show algebraMap R S t ^ m = 0 by simpa using e]

Result:
no goals

Proof state:
case pos
R S : Type u_1
inst✝¹ : CommRing R
inst✝ : CommRing S
f : R →+* S
s : Set R
hs : Ideal.span s = ⊤
H : ∀ (r : ↑s), (fun {R S} [CommRing R] [CommRing S] x => x.IsIntegral) (Localization.awayMap f ↑r)
r : S
this✝³ : Algebra R S := f.toAlgebra
t : R
ht : t ∈ s
this✝² : Algebra (Localization.Away t) (Localization.Away (f t)) := (Localization.awayMap f t).toAlgebra
this✝¹ : IsScalarTower R (Localization.Away t) (Localization.Away (f t))
this✝ : _root_.IsIntegral (Localization.Away t) ((algebraMap S (Localization.Away (f t))) r)
n : ℕ
p : R[X]
hp : p.Monic
m : ℕ
e : ↑⟨(algebraMap R S) t ^ m, ⋯⟩ * eval₂ (algebraMap R S) ((algebraMap R S) ↑⟨(fun x => t ^ x) n, ⋯⟩ * r) p = 0
hp' : 1 ≤ p.natDegree
this :
  eval₂ (algebraMap R S) ((algebraMap R S) (t ^ m) * t ^ n • r) (p.scaleRoots (t ^ m)) =
    (algebraMap R S) (t ^ m) ^ p.natDegree * eval₂ (algebraMap R S) (t ^ n • r) p
⊢ eval₂ (algebraMap R S) (↑⟨t, ht⟩ ^ (m + n) • r) (p.scaleRoots (t ^ m)) = 0

Tactic:
simp only [pow_add, ← Algebra.smul_def, mul_smul, ← map_pow] at e this ⊢

Result:
case pos
R S : Type u_1
inst✝¹ : CommRing R
inst✝ : CommRing S
f : R →+* S
s : Set R
hs : Ideal.span s = ⊤
H : ∀ (r : ↑s), (fun {R S} [CommRing R] [CommRing S] x => x.IsIntegral) (Localization.awayMap f ↑r)
r : S
this✝³ : Algebra R S := f.toAlgebra
t : R
ht : t ∈ s
this✝² : Algebra (Localization.Away t) (Localization.Away (f t)) := (Localization.awayMap f t).toAlgebra
this✝¹ : IsScalarTower R (Localization.Away t) (Localization.Away (f t))
this✝ : _root_.IsIntegral (Localization.Away t) ((algebraMap S (Localization.Away (f t))) r)
n : ℕ
p : R[X]
hp : p.Monic
m : ℕ
hp' : 1 ≤ p.natDegree
e : t ^ m • eval₂ (algebraMap R S) (t ^ n • r) p = 0
this :
  eval₂ (algebraMap R S) (t ^ m • t ^ n • r) (p.scaleRoots (t ^ m)) =
    (t ^ m) ^ p.natDegree • eval₂ (algebraMap R S) (t ^ n • r) p
⊢ eval₂ (algebraMap R S) (t ^ m • t ^ n • r) (p.scaleRoots (t ^ m)) = 0

Proof state:
R S : Type u_1
inst✝¹ : CommRing R
inst✝ : CommRing S
f : R →+* S
s : Set R
hs : Ideal.span s = ⊤
H : ∀ (r : ↑s), (fun {R S} [CommRing R] [CommRing S] x => x.IsIntegral) (Localization.awayMap f ↑r)
r : S
this : Algebra R S := f.toAlgebra
⊢ f.IsIntegralElem r

Tactic:
show r ∈ (integralClosure R S).toSubmodule

Result:
R S : Type u_1
inst✝¹ : CommRing R
inst✝ : CommRing S
f : R →+* S
s : Set R
hs : Ideal.span s = ⊤
H : ∀ (r : ↑s), (fun {R S} [CommRing R] [CommRing S] x => x.IsIntegral) (Localization.awayMap f ↑r)
r : S
this : Algebra R S := f.toAlgebra
⊢ r ∈ Subalgebra.toSubmodule (integralClosure R S)

Proof state:
case neg
R S : Type u_1
inst✝¹ : CommRing R
inst✝ : CommRing S
f : R →+* S
s : Set R
hs : Ideal.span s = ⊤
H : ∀ (r : ↑s), (fun {R S} [CommRing R] [CommRing S] x => x.IsIntegral) (Localization.awayMap f ↑r)
r : S
this✝² : Algebra R S := f.toAlgebra
t : R
ht : t ∈ s
this✝¹ : Algebra (Localization.Away t) (Localization.Away (f t)) := (Localization.awayMap f t).toAlgebra
this✝ : IsScalarTower R (Localization.Away t) (Localization.Away (f t))
this : _root_.IsIntegral (Localization.Away t) ((algebraMap S (Localization.Away (f t))) r)
n m : ℕ
hp : Monic 1
e : ↑⟨(algebraMap R S) t ^ m, ⋯⟩ * eval₂ (algebraMap R S) ((algebraMap R S) ↑⟨(fun x => t ^ x) n, ⋯⟩ * r) 1 = 0
hp' : ¬1 ≤ natDegree 1
⊢ ∃ n, ↑⟨t, ht⟩ ^ n • r ∈ Subalgebra.toSubmodule (integralClosure R S)

Tactic:
exact ⟨m, by simp [Algebra.smul_def, show algebraMap R S t ^ m = 0 by simpa using e]⟩

Result:
no goals

Proof state:
case pos
R S : Type u_1
inst✝¹ : CommRing R
inst✝ : CommRing S
f : R →+* S
s : Set R
hs : Ideal.span s = ⊤
H : ∀ (r : ↑s), (fun {R S} [CommRing R] [CommRing S] x => x.IsIntegral) (Localization.awayMap f ↑r)
r : S
this✝² : Algebra R S := f.toAlgebra
t : R
ht : t ∈ s
this✝¹ : Algebra (Localization.Away t) (Localization.Away (f t)) := (Localization.awayMap f t).toAlgebra
this✝ : IsScalarTower R (Localization.Away t) (Localization.Away (f t))
this : _root_.IsIntegral (Localization.Away t) ((algebraMap S (Localization.Away (f t))) r)
n : ℕ
p : R[X]
hp : p.Monic
m : ℕ
e : ↑⟨(algebraMap R S) t ^ m, ⋯⟩ * eval₂ (algebraMap R S) ((algebraMap R S) ↑⟨(fun x => t ^ x) n, ⋯⟩ * r) p = 0
hp' : 1 ≤ p.natDegree
⊢ eval₂ (algebraMap R S) (↑⟨t, ht⟩ ^ (m + n) • r) (p.scaleRoots (t ^ m)) = 0

Tactic:
have := p.scaleRoots_eval₂_mul (algebraMap R S) (t ^ n • r) (t ^ m)

Result:
case pos
R S : Type u_1
inst✝¹ : CommRing R
inst✝ : CommRing S
f : R →+* S
s : Set R
hs : Ideal.span s = ⊤
H : ∀ (r : ↑s), (fun {R S} [CommRing R] [CommRing S] x => x.IsIntegral) (Localization.awayMap f ↑r)
r : S
this✝³ : Algebra R S := f.toAlgebra
t : R
ht : t ∈ s
this✝² : Algebra (Localization.Away t) (Localization.Away (f t)) := (Localization.awayMap f t).toAlgebra
this✝¹ : IsScalarTower R (Localization.Away t) (Localization.Away (f t))
this✝ : _root_.IsIntegral (Localization.Away t) ((algebraMap S (Localization.Away (f t))) r)
n : ℕ
p : R[X]
hp : p.Monic
m : ℕ
e : ↑⟨(algebraMap R S) t ^ m, ⋯⟩ * eval₂ (algebraMap R S) ((algebraMap R S) ↑⟨(fun x => t ^ x) n, ⋯⟩ * r) p = 0
hp' : 1 ≤ p.natDegree
this :
  eval₂ (algebraMap R S) ((algebraMap R S) (t ^ m) * t ^ n • r) (p.scaleRoots (t ^ m)) =
    (algebraMap R S) (t ^ m) ^ p.natDegree * eval₂ (algebraMap R S) (t ^ n • r) p
⊢ eval₂ (algebraMap R S) (↑⟨t, ht⟩ ^ (m + n) • r) (p.scaleRoots (t ^ m)) = 0