-- Mathlib/RingTheory/Algebraic/Integral.lean
theorem restrictScalars [Algebra.IsAlgebraic R S]
    {a : A} (h : IsAlgebraic S a) : IsAlgebraic R a

Proof state:
R : Type u_1
S : Type u_2
A : Type u_3
inst✝⁸ : CommRing R
inst✝⁷ : CommRing S
inst✝⁶ : Ring A
inst✝⁵ : Algebra R S
inst✝⁴ : Algebra R A
inst✝³ : Algebra S A
inst✝² : IsScalarTower R S A
inst✝¹ : NoZeroDivisors S
inst✝ : Algebra.IsAlgebraic R S
a : A
h : IsAlgebraic S a
⊢ IsAlgebraic R a

Tactic:
have ⟨p, hp, eval0⟩ := h

Result:
R : Type u_1
S : Type u_2
A : Type u_3
inst✝⁸ : CommRing R
inst✝⁷ : CommRing S
inst✝⁶ : Ring A
inst✝⁵ : Algebra R S
inst✝⁴ : Algebra R A
inst✝³ : Algebra S A
inst✝² : IsScalarTower R S A
inst✝¹ : NoZeroDivisors S
inst✝ : Algebra.IsAlgebraic R S
a : A
h : IsAlgebraic S a
p : S[X]
hp : p ≠ 0
eval0 : (aeval a) p = 0
⊢ IsAlgebraic R a

Proof state:
case refine_2
R : Type u_1
S : Type u_2
A : Type u_3
inst✝⁸ : CommRing R
inst✝⁷ : CommRing S
inst✝⁶ : Ring A
inst✝⁵ : Algebra R S
inst✝⁴ : Algebra R A
inst✝³ : Algebra S A
inst✝² : IsScalarTower R S A
inst✝¹ : NoZeroDivisors S
inst✝ : Algebra.IsAlgebraic R S
a : A
h : IsAlgebraic S a
p✝ : S[X]
hp : p✝ ≠ 0
eval0 : (aeval a) p✝ = 0
hRS : Function.Injective ⇑(algebraMap R S)
this : NoZeroDivisors R
r : R
hr : r ≠ 0
int : ∀ z ∈ Finset.image p✝.coeff p✝.support, IsIntegral R (r • z)
p : (↥(integralClosure R S).toSubring)[X] := (r • p✝).toSubring (integralClosure R S).toSubring ⋯
⊢ (aeval a) p = 0

Tactic:
rw [← eval_map_algebraMap, Subalgebra.algebraMap_eq, ← map_map, ← Subalgebra.toSubring_subtype,
  map_toSubring, eval_map_algebraMap, ← AlgHom.restrictScalars_apply R,
  map_smul, AlgHom.restrictScalars_apply, eval0, smul_zero]

Result:
no goals

Proof state:
R : Type u_1
S : Type u_2
A : Type u_3
inst✝⁸ : CommRing R
inst✝⁷ : CommRing S
inst✝⁶ : Ring A
inst✝⁵ : Algebra R S
inst✝⁴ : Algebra R A
inst✝³ : Algebra S A
inst✝² : IsScalarTower R S A
inst✝¹ : NoZeroDivisors S
inst✝ : Algebra.IsAlgebraic R S
a : A
h : IsAlgebraic S a
p✝ : S[X]
hp : p✝ ≠ 0
eval0 : (aeval a) p✝ = 0
hRS : Function.Injective ⇑(algebraMap R S)
this : NoZeroDivisors R
r : R
hr : r ≠ 0
int : ∀ z ∈ Finset.image p✝.coeff p✝.support, IsIntegral R (r • z)
p : (↥(integralClosure R S).toSubring)[X] := (r • p✝).toSubring (integralClosure R S).toSubring ⋯
⊢ IsAlgebraic (↥(integralClosure R S)) a

Tactic:
refine ⟨p, ?_, ?_⟩

Result:
case refine_1
R : Type u_1
S : Type u_2
A : Type u_3
inst✝⁸ : CommRing R
inst✝⁷ : CommRing S
inst✝⁶ : Ring A
inst✝⁵ : Algebra R S
inst✝⁴ : Algebra R A
inst✝³ : Algebra S A
inst✝² : IsScalarTower R S A
inst✝¹ : NoZeroDivisors S
inst✝ : Algebra.IsAlgebraic R S
a : A
h : IsAlgebraic S a
p✝ : S[X]
hp : p✝ ≠ 0
eval0 : (aeval a) p✝ = 0
hRS : Function.Injective ⇑(algebraMap R S)
this : NoZeroDivisors R
r : R
hr : r ≠ 0
int : ∀ z ∈ Finset.image p✝.coeff p✝.support, IsIntegral R (r • z)
p : (↥(integralClosure R S).toSubring)[X] := (r • p✝).toSubring (integralClosure R S).toSubring ⋯
⊢ p ≠ 0

case refine_2
R : Type u_1
S : Type u_2
A : Type u_3
inst✝⁸ : CommRing R
inst✝⁷ : CommRing S
inst✝⁶ : Ring A
inst✝⁵ : Algebra R S
inst✝⁴ : Algebra R A
inst✝³ : Algebra S A
inst✝² : IsScalarTower R S A
inst✝¹ : NoZeroDivisors S
inst✝ : Algebra.IsAlgebraic R S
a : A
h : IsAlgebraic S a
p✝ : S[X]
hp : p✝ ≠ 0
eval0 : (aeval a) p✝ = 0
hRS : Function.Injective ⇑(algebraMap R S)
this : NoZeroDivisors R
r : R
hr : r ≠ 0
int : ∀ z ∈ Finset.image p✝.coeff p✝.support, IsIntegral R (r • z)
p : (↥(integralClosure R S).toSubring)[X] := (r • p✝).toSubring (integralClosure R S).toSubring ⋯
⊢ (aeval a) p = 0

Proof state:
case refine_1
R : Type u_1
S : Type u_2
A : Type u_3
inst✝⁸ : CommRing R
inst✝⁷ : CommRing S
inst✝⁶ : Ring A
inst✝⁵ : Algebra R S
inst✝⁴ : Algebra R A
inst✝³ : Algebra S A
inst✝² : IsScalarTower R S A
inst✝¹ : NoZeroDivisors S
inst✝ : Algebra.IsAlgebraic R S
a : A
h : IsAlgebraic S a
p✝ : S[X]
hp : p✝ ≠ 0
eval0 : (aeval a) p✝ = 0
hRS : Function.Injective ⇑(algebraMap R S)
this✝ : NoZeroDivisors R
r : R
hr : r ≠ 0
int : ∀ z ∈ Finset.image p✝.coeff p✝.support, IsIntegral R (r • z)
p : (↥(integralClosure R S).toSubring)[X] := (r • p✝).toSubring (integralClosure R S).toSubring ⋯
this : FaithfulSMul R S
⊢ p ≠ 0

Tactic:
simpa only [← Polynomial.map_ne_zero_iff (f := Subring.subtype _) Subtype.val_injective,
  p, map_toSubring, smul_ne_zero_iff] using And.intro hr hp

Result:
no goals

Proof state:
R : Type u_1
S : Type u_2
A : Type u_3
inst✝⁸ : CommRing R
inst✝⁷ : CommRing S
inst✝⁶ : Ring A
inst✝⁵ : Algebra R S
inst✝⁴ : Algebra R A
inst✝³ : Algebra S A
inst✝² : IsScalarTower R S A
inst✝¹ : NoZeroDivisors S
inst✝ : Algebra.IsAlgebraic R S
a : A
h : IsAlgebraic S a
p : S[X]
hp : p ≠ 0
eval0 : (aeval a) p = 0
⊢ IsAlgebraic R a

Tactic:
by_cases hRS : Function.Injective (algebraMap R S)

Result:
case pos
R : Type u_1
S : Type u_2
A : Type u_3
inst✝⁸ : CommRing R
inst✝⁷ : CommRing S
inst✝⁶ : Ring A
inst✝⁵ : Algebra R S
inst✝⁴ : Algebra R A
inst✝³ : Algebra S A
inst✝² : IsScalarTower R S A
inst✝¹ : NoZeroDivisors S
inst✝ : Algebra.IsAlgebraic R S
a : A
h : IsAlgebraic S a
p : S[X]
hp : p ≠ 0
eval0 : (aeval a) p = 0
hRS : Function.Injective ⇑(algebraMap R S)
⊢ IsAlgebraic R a

case neg
R : Type u_1
S : Type u_2
A : Type u_3
inst✝⁸ : CommRing R
inst✝⁷ : CommRing S
inst✝⁶ : Ring A
inst✝⁵ : Algebra R S
inst✝⁴ : Algebra R A
inst✝³ : Algebra S A
inst✝² : IsScalarTower R S A
inst✝¹ : NoZeroDivisors S
inst✝ : Algebra.IsAlgebraic R S
a : A
h : IsAlgebraic S a
p : S[X]
hp : p ≠ 0
eval0 : (aeval a) p = 0
hRS : ¬Function.Injective ⇑(algebraMap R S)
⊢ IsAlgebraic R a

Proof state:
case pos
R : Type u_1
S : Type u_2
A : Type u_3
inst✝⁸ : CommRing R
inst✝⁷ : CommRing S
inst✝⁶ : Ring A
inst✝⁵ : Algebra R S
inst✝⁴ : Algebra R A
inst✝³ : Algebra S A
inst✝² : IsScalarTower R S A
inst✝¹ : NoZeroDivisors S
inst✝ : Algebra.IsAlgebraic R S
a : A
h : IsAlgebraic S a
p : S[X]
hp : p ≠ 0
eval0 : (aeval a) p = 0
hRS : Function.Injective ⇑(algebraMap R S)
this : NoZeroDivisors R
⊢ IsAlgebraic R a

Tactic:
have ⟨r, hr, int⟩ := Algebra.IsAlgebraic.exists_integral_multiples R (p.support.image (coeff p))

Result:
case pos
R : Type u_1
S : Type u_2
A : Type u_3
inst✝⁸ : CommRing R
inst✝⁷ : CommRing S
inst✝⁶ : Ring A
inst✝⁵ : Algebra R S
inst✝⁴ : Algebra R A
inst✝³ : Algebra S A
inst✝² : IsScalarTower R S A
inst✝¹ : NoZeroDivisors S
inst✝ : Algebra.IsAlgebraic R S
a : A
h : IsAlgebraic S a
p : S[X]
hp : p ≠ 0
eval0 : (aeval a) p = 0
hRS : Function.Injective ⇑(algebraMap R S)
this : NoZeroDivisors R
r : R
hr : r ≠ 0
int : ∀ z ∈ Finset.image p.coeff p.support, IsIntegral R (r • z)
⊢ IsAlgebraic R a

Proof state:
case intro.intro
R : Type u_1
S : Type u_2
A : Type u_3
inst✝⁸ : CommRing R
inst✝⁷ : CommRing S
inst✝⁶ : Ring A
inst✝⁵ : Algebra R S
inst✝⁴ : Algebra R A
inst✝³ : Algebra S A
inst✝² : IsScalarTower R S A
inst✝¹ : NoZeroDivisors S
inst✝ : Algebra.IsAlgebraic R S
a : A
h : IsAlgebraic S a
p : S[X]
hp : p ≠ 0
eval0 : (aeval a) p = 0
hRS : Function.Injective ⇑(algebraMap R S)
this : NoZeroDivisors R
r : R
hr : r ≠ 0
int : ∀ z ∈ Finset.image p.coeff p.support, IsIntegral R (r • z)
n : ℕ
hn : n ∈ (r • p).support
hs : (r • p).coeff n ∈ ↑(r • p).coeffs
⊢ (r • p).coeff n ∈ ↑(integralClosure R S).toSubring

Tactic:
exact int _ (Finset.mem_image_of_mem _ <| support_smul _ _ hn)

Result:
no goals