Theorem: Field.primitive_element_inf_aux
File: Mathlib/FieldTheory/PrimitiveElement.lean

tactic: have hα := IsSeparable.isIntegral F α
state_before: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
⊢ ∃ γ, F⟮α, β⟯ = F⟮γ⟯
state_after: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
⊢ ∃ γ, F⟮α, β⟯ = F⟮γ⟯

tactic: have hβ := IsSeparable.isIntegral F β
state_before: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
⊢ ∃ γ, F⟮α, β⟯ = F⟮γ⟯
state_after: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
⊢ ∃ γ, F⟮α, β⟯ = F⟮γ⟯

tactic: let f := minpoly F α
state_before: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
⊢ ∃ γ, F⟮α, β⟯ = F⟮γ⟯
state_after: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
⊢ ∃ γ, F⟮α, β⟯ = F⟮γ⟯

tactic: let g := minpoly F β
state_before: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
⊢ ∃ γ, F⟮α, β⟯ = F⟮γ⟯
state_after: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
⊢ ∃ γ, F⟮α, β⟯ = F⟮γ⟯

tactic: let ιFE := algebraMap F E
state_before: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
⊢ ∃ γ, F⟮α, β⟯ = F⟮γ⟯
state_after: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
⊢ ∃ γ, F⟮α, β⟯ = F⟮γ⟯

tactic: let ιEE' := algebraMap E (SplittingField (g.map ιFE))
state_before: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
⊢ ∃ γ, F⟮α, β⟯ = F⟮γ⟯
state_after: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
⊢ ∃ γ, F⟮α, β⟯ = F⟮γ⟯

tactic: obtain ⟨c, hc⟩ := primitive_element_inf_aux_exists_c (ιEE'.comp ιFE) (ιEE' α) (ιEE' β) f g
state_before: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
⊢ ∃ γ, F⟮α, β⟯ = F⟮γ⟯
state_after: case intro
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
⊢ ∃ γ, F⟮α, β⟯ = F⟮γ⟯

tactic: let γ := α + c • β
state_before: case intro
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
⊢ ∃ γ, F⟮α, β⟯ = F⟮γ⟯
state_after: case intro
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
⊢ ∃ γ, F⟮α, β⟯ = F⟮γ⟯

tactic: let p := EuclideanDomain.gcd ((f.map (algebraMap F F⟮γ⟯)).comp
  (C (AdjoinSimple.gen F γ) - (C ↑c : F⟮γ⟯[X]) * X)) (g.map (algebraMap F F⟮γ⟯))
state_before: case intro
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
⊢ β ∈ F⟮γ⟯
state_after: case intro
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
⊢ β ∈ F⟮γ⟯

tactic: let h := EuclideanDomain.gcd ((f.map ιFE).comp (C γ - C (ιFE c) * X)) (g.map ιFE)
state_before: case intro
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
⊢ β ∈ F⟮γ⟯
state_after: case intro
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
⊢ β ∈ F⟮γ⟯

tactic: have map_g_ne_zero : g.map ιFE ≠ 0 := map_ne_zero (minpoly.ne_zero hβ)
state_before: case intro
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
⊢ β ∈ F⟮γ⟯
state_after: case intro
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
⊢ β ∈ F⟮γ⟯

tactic: have h_ne_zero : h ≠ 0 :=
  mt EuclideanDomain.gcd_eq_zero_iff.mp (not_and.mpr fun _ => map_g_ne_zero)
state_before: case intro
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
⊢ β ∈ F⟮γ⟯
state_after: case intro
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
⊢ β ∈ F⟮γ⟯

tactic: suffices p_linear : p.map (algebraMap F⟮γ⟯ E) = C h.leadingCoeff * (X - C β) by
  have finale : β = algebraMap F⟮γ⟯ E (-p.coeff 0 / p.coeff 1) := by
    rw [map_div₀, RingHom.map_neg, ← coeff_map, ← coeff_map, p_linear]
    simp [mul_sub, coeff_C, mul_div_cancel_left₀ β (mt leadingCoeff_eq_zero.mp h_ne_zero),
      -map_add]
    rw [finale]
  exact Subtype.mem (-p.coeff 0 / p.coeff 1)
state_before: case intro
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
⊢ β ∈ F⟮γ⟯
state_after: case intro
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
⊢ Polynomial.map (algebraMap (↥F⟮γ⟯) E) p = C h.leadingCoeff * (X - C β)

tactic: have h_sep : h.Separable := separable_gcd_right _ (IsSeparable.separable F β).map
state_before: case intro
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
⊢ Polynomial.map (algebraMap (↥F⟮γ⟯) E) p = C h.leadingCoeff * (X - C β)
state_after: case intro
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
⊢ Polynomial.map (algebraMap (↥F⟮γ⟯) E) p = C h.leadingCoeff * (X - C β)

tactic: have h_splits : Splits ιEE' h :=
  splits_of_splits_gcd_right ιEE' map_g_ne_zero (SplittingField.splits _)
state_before: case intro
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
h_root : eval β h = 0
⊢ Polynomial.map (algebraMap (↥F⟮γ⟯) E) p = C h.leadingCoeff * (X - C β)
state_after: case intro
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
h_root : eval β h = 0
h_splits : Splits ιEE' h
⊢ Polynomial.map (algebraMap (↥F⟮γ⟯) E) p = C h.leadingCoeff * (X - C β)

tactic: have h_roots : ∀ x ∈ (h.map ιEE').roots, x = ιEE' β := by
  intro x hx
  rw [mem_roots_map h_ne_zero] at hx
  specialize hc (ιEE' γ - ιEE' (ιFE c) * x) (by
    have f_root := root_left_of_root_gcd hx
    rw [eval₂_comp, eval₂_sub, eval₂_mul, eval₂_C, eval₂_C, eval₂_X, eval₂_map] at f_root
    exact (mem_roots_map (minpoly.ne_zero hα)).mpr f_root)
  specialize hc x (by
    rw [mem_roots_map (minpoly.ne_zero hβ), ← eval₂_map]
    exact root_right_of_root_gcd hx)
  by_contra a
  apply hc
  apply (div_eq_iff (sub_ne_zero.mpr a)).mpr
  simp only [γ, Algebra.smul_def, RingHom.map_add, RingHom.map_mul, RingHom.comp_apply]
  ring
state_before: case intro
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
h_root : eval β h = 0
h_splits : Splits ιEE' h
⊢ Polynomial.map (algebraMap (↥F⟮γ⟯) E) p = C h.leadingCoeff * (X - C β)
state_after: case intro
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
h_root : eval β h = 0
h_splits : Splits ιEE' h
h_roots : ∀ x ∈ (Polynomial.map ιEE' h).roots, x = ιEE' β
⊢ Polynomial.map (algebraMap (↥F⟮γ⟯) E) p = C h.leadingCoeff * (X - C β)

tactic: rw [← eq_X_sub_C_of_separable_of_root_eq h_sep h_root h_splits h_roots]
state_before: case intro
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
h_root : eval β h = 0
h_splits : Splits ιEE' h
h_roots : ∀ x ∈ (Polynomial.map ιEE' h).roots, x = ιEE' β
⊢ Polynomial.map (algebraMap (↥F⟮γ⟯) E) p = C h.leadingCoeff * (X - C β)
state_after: case intro
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
h_root : eval β h = 0
h_splits : Splits ιEE' h
h_roots : ∀ x ∈ (Polynomial.map ιEE' h).roots, x = ιEE' β
⊢ Polynomial.map (algebraMap (↥F⟮γ⟯) E) p = h

tactic: trans EuclideanDomain.gcd (?_ : E[X]) (?_ : E[X])
state_before: case intro
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
h_root : eval β h = 0
h_splits : Splits ιEE' h
h_roots : ∀ x ∈ (Polynomial.map ιEE' h).roots, x = ιEE' β
⊢ Polynomial.map (algebraMap (↥F⟮γ⟯) E) p = h
state_after: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
h_root : eval β h = 0
h_splits : Splits ιEE' h
h_roots : ∀ x ∈ (Polynomial.map ιEE' h).roots, x = ιEE' β
⊢ Polynomial.map (algebraMap (↥F⟮γ⟯) E) p = EuclideanDomain.gcd ?intro.intro_1 ?intro.intro_2

F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
h_root : eval β h = 0
h_splits : Splits ιEE' h
h_roots : ∀ x ∈ (Polynomial.map ιEE' h).roots, x = ιEE' β
⊢ EuclideanDomain.gcd ?intro.intro_1 ?intro.intro_2 = h

case intro.intro_1
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
h_root : eval β h = 0
h_splits : Splits ιEE' h
h_roots : ∀ x ∈ (Polynomial.map ιEE' h).roots, x = ιEE' β
⊢ E[X]

case intro.intro_2
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
h_root : eval β h = 0
h_splits : Splits ιEE' h
h_roots : ∀ x ∈ (Polynomial.map ιEE' h).roots, x = ιEE' β
⊢ E[X]

tactic: use γ
state_before: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
β_in_Fγ : β ∈ F⟮γ⟯
⊢ ∃ γ, F⟮α, β⟯ = F⟮γ⟯
state_after: case h
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
β_in_Fγ : β ∈ F⟮γ⟯
⊢ F⟮α, β⟯ = F⟮γ⟯

tactic: apply le_antisymm
state_before: case h
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
β_in_Fγ : β ∈ F⟮γ⟯
⊢ F⟮α, β⟯ = F⟮γ⟯
state_after: case h.a
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
β_in_Fγ : β ∈ F⟮γ⟯
⊢ F⟮α, β⟯ ≤ F⟮γ⟯

case h.a
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
β_in_Fγ : β ∈ F⟮γ⟯
⊢ F⟮γ⟯ ≤ F⟮α, β⟯

tactic: rw [adjoin_le_iff]
state_before: case h.a
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
β_in_Fγ : β ∈ F⟮γ⟯
⊢ F⟮α, β⟯ ≤ F⟮γ⟯
state_after: case h.a
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
β_in_Fγ : β ∈ F⟮γ⟯
⊢ {α, β} ≤ ↑F⟮γ⟯

tactic: have α_in_Fγ : α ∈ F⟮γ⟯ := by
  rw [← add_sub_cancel_right α (c • β)]
  exact F⟮γ⟯.sub_mem (mem_adjoin_simple_self F γ) (F⟮γ⟯.toSubalgebra.smul_mem β_in_Fγ c)
state_before: case h.a
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
β_in_Fγ : β ∈ F⟮γ⟯
⊢ {α, β} ≤ ↑F⟮γ⟯
state_after: case h.a
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
β_in_Fγ : β ∈ F⟮γ⟯
α_in_Fγ : α ∈ F⟮γ⟯
⊢ {α, β} ≤ ↑F⟮γ⟯

tactic: rintro x (rfl | rfl) <;> assumption
state_before: case h.a
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
β_in_Fγ : β ∈ F⟮γ⟯
α_in_Fγ : α ∈ F⟮γ⟯
⊢ {α, β} ≤ ↑F⟮γ⟯
state_after: no goals

tactic: rw [← add_sub_cancel_right α (c • β)]
state_before: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
β_in_Fγ : β ∈ F⟮γ⟯
⊢ α ∈ F⟮γ⟯
state_after: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
β_in_Fγ : β ∈ F⟮γ⟯
⊢ α + c • β - c • β ∈ F⟮γ⟯

tactic: exact F⟮γ⟯.sub_mem (mem_adjoin_simple_self F γ) (F⟮γ⟯.toSubalgebra.smul_mem β_in_Fγ c)
state_before: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
β_in_Fγ : β ∈ F⟮γ⟯
⊢ α + c • β - c • β ∈ F⟮γ⟯
state_after: no goals

tactic: rw [adjoin_simple_le_iff]
state_before: case h.a
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
β_in_Fγ : β ∈ F⟮γ⟯
⊢ F⟮γ⟯ ≤ F⟮α, β⟯
state_after: case h.a
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
β_in_Fγ : β ∈ F⟮γ⟯
⊢ γ ∈ F⟮α, β⟯

tactic: have α_in_Fαβ : α ∈ F⟮α, β⟯ := subset_adjoin F {α, β} (Set.mem_insert α {β})
state_before: case h.a
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
β_in_Fγ : β ∈ F⟮γ⟯
⊢ γ ∈ F⟮α, β⟯
state_after: case h.a
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
β_in_Fγ : β ∈ F⟮γ⟯
α_in_Fαβ : α ∈ F⟮α, β⟯
⊢ γ ∈ F⟮α, β⟯

tactic: have β_in_Fαβ : β ∈ F⟮α, β⟯ := subset_adjoin F {α, β} (Set.mem_insert_of_mem α rfl)
state_before: case h.a
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
β_in_Fγ : β ∈ F⟮γ⟯
α_in_Fαβ : α ∈ F⟮α, β⟯
⊢ γ ∈ F⟮α, β⟯
state_after: case h.a
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
β_in_Fγ : β ∈ F⟮γ⟯
α_in_Fαβ : α ∈ F⟮α, β⟯
β_in_Fαβ : β ∈ F⟮α, β⟯
⊢ γ ∈ F⟮α, β⟯

tactic: exact F⟮α, β⟯.add_mem α_in_Fαβ (F⟮α, β⟯.smul_mem β_in_Fαβ)
state_before: case h.a
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
β_in_Fγ : β ∈ F⟮γ⟯
α_in_Fαβ : α ∈ F⟮α, β⟯
β_in_Fαβ : β ∈ F⟮α, β⟯
⊢ γ ∈ F⟮α, β⟯
state_after: no goals

tactic: have finale : β = algebraMap F⟮γ⟯ E (-p.coeff 0 / p.coeff 1) := by
  rw [map_div₀, RingHom.map_neg, ← coeff_map, ← coeff_map, p_linear]
  simp [mul_sub, coeff_C, mul_div_cancel_left₀ β (mt leadingCoeff_eq_zero.mp h_ne_zero),
    -map_add]
state_before: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
p_linear : Polynomial.map (algebraMap (↥F⟮γ⟯) E) p = C h.leadingCoeff * (X - C β)
⊢ β ∈ F⟮γ⟯
state_after: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
p_linear : Polynomial.map (algebraMap (↥F⟮γ⟯) E) p = C h.leadingCoeff * (X - C β)
finale : β = (algebraMap (↥F⟮γ⟯) E) (-p.coeff 0 / p.coeff 1)
⊢ β ∈ F⟮γ⟯

tactic: rw [finale]
state_before: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
p_linear : Polynomial.map (algebraMap (↥F⟮γ⟯) E) p = C h.leadingCoeff * (X - C β)
finale : β = (algebraMap (↥F⟮γ⟯) E) (-p.coeff 0 / p.coeff 1)
⊢ β ∈ F⟮γ⟯
state_after: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
p_linear : Polynomial.map (algebraMap (↥F⟮γ⟯) E) p = C h.leadingCoeff * (X - C β)
finale : β = (algebraMap (↥F⟮γ⟯) E) (-p.coeff 0 / p.coeff 1)
⊢ (algebraMap (↥F⟮γ⟯) E) (-p.coeff 0 / p.coeff 1) ∈ F⟮γ⟯

tactic: exact Subtype.mem (-p.coeff 0 / p.coeff 1)
state_before: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
p_linear : Polynomial.map (algebraMap (↥F⟮γ⟯) E) p = C h.leadingCoeff * (X - C β)
finale : β = (algebraMap (↥F⟮γ⟯) E) (-p.coeff 0 / p.coeff 1)
⊢ (algebraMap (↥F⟮γ⟯) E) (-p.coeff 0 / p.coeff 1) ∈ F⟮γ⟯
state_after: no goals

tactic: rw [map_div₀, RingHom.map_neg, ← coeff_map, ← coeff_map, p_linear]
state_before: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
p_linear : Polynomial.map (algebraMap (↥F⟮γ⟯) E) p = C h.leadingCoeff * (X - C β)
⊢ β = (algebraMap (↥F⟮γ⟯) E) (-p.coeff 0 / p.coeff 1)
state_after: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
p_linear : Polynomial.map (algebraMap (↥F⟮γ⟯) E) p = C h.leadingCoeff * (X - C β)
⊢ β = -(C h.leadingCoeff * (X - C β)).coeff 0 / (C h.leadingCoeff * (X - C β)).coeff 1

tactic: simp [mul_sub, coeff_C, mul_div_cancel_left₀ β (mt leadingCoeff_eq_zero.mp h_ne_zero),
  -map_add]
state_before: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
p_linear : Polynomial.map (algebraMap (↥F⟮γ⟯) E) p = C h.leadingCoeff * (X - C β)
⊢ β = -(C h.leadingCoeff * (X - C β)).coeff 0 / (C h.leadingCoeff * (X - C β)).coeff 1
state_after: no goals

tactic: apply eval_gcd_eq_zero
state_before: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
⊢ eval β h = 0
state_after: case hf
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
⊢ eval β ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) = 0

case hg
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
⊢ eval β (Polynomial.map ιFE g) = 0

tactic: rw [eval_comp, eval_sub, eval_mul, eval_C, eval_C, eval_X, eval_map, ← aeval_def, ←
  Algebra.smul_def, add_sub_cancel_right, minpoly.aeval]
state_before: case hf
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
⊢ eval β ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) = 0
state_after: no goals

tactic: rw [eval_map, ← aeval_def, minpoly.aeval]
state_before: case hg
F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
⊢ eval β (Polynomial.map ιFE g) = 0
state_after: no goals

tactic: intro x hx
state_before: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
h_root : eval β h = 0
h_splits : Splits ιEE' h
⊢ ∀ x ∈ (Polynomial.map ιEE' h).roots, x = ιEE' β
state_after: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
h_root : eval β h = 0
h_splits : Splits ιEE' h
x : (Polynomial.map ιFE g).SplittingField
hx : x ∈ (Polynomial.map ιEE' h).roots
⊢ x = ιEE' β

tactic: rw [mem_roots_map h_ne_zero] at hx
state_before: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
h_root : eval β h = 0
h_splits : Splits ιEE' h
x : (Polynomial.map ιFE g).SplittingField
hx : x ∈ (Polynomial.map ιEE' h).roots
⊢ x = ιEE' β
state_after: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
h_root : eval β h = 0
h_splits : Splits ιEE' h
x : (Polynomial.map ιFE g).SplittingField
hx : eval₂ ιEE' x h = 0
⊢ x = ιEE' β

tactic: specialize hc (ιEE' γ - ιEE' (ιFE c) * x) (by
  have f_root := root_left_of_root_gcd hx
  rw [eval₂_comp, eval₂_sub, eval₂_mul, eval₂_C, eval₂_C, eval₂_X, eval₂_map] at f_root
  exact (mem_roots_map (minpoly.ne_zero hα)).mpr f_root)
state_before: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
h_root : eval β h = 0
h_splits : Splits ιEE' h
x : (Polynomial.map ιFE g).SplittingField
hx : eval₂ ιEE' x h = 0
⊢ x = ιEE' β
state_after: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
h_root : eval β h = 0
h_splits : Splits ιEE' h
x : (Polynomial.map ιFE g).SplittingField
hx : eval₂ ιEE' x h = 0
hc :
  ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots,
    -(ιEE' γ - ιEE' (ιFE c) * x - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
⊢ x = ιEE' β

tactic: specialize hc x (by
  rw [mem_roots_map (minpoly.ne_zero hβ), ← eval₂_map]
  exact root_right_of_root_gcd hx)
state_before: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
h_root : eval β h = 0
h_splits : Splits ιEE' h
x : (Polynomial.map ιFE g).SplittingField
hx : eval₂ ιEE' x h = 0
hc :
  ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots,
    -(ιEE' γ - ιEE' (ιFE c) * x - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
⊢ x = ιEE' β
state_after: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
h_root : eval β h = 0
h_splits : Splits ιEE' h
x : (Polynomial.map ιFE g).SplittingField
hx : eval₂ ιEE' x h = 0
hc : -(ιEE' γ - ιEE' (ιFE c) * x - ιEE' α) / (x - ιEE' β) ≠ (ιEE'.comp ιFE) c
⊢ x = ιEE' β

tactic: by_contra a
state_before: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
h_root : eval β h = 0
h_splits : Splits ιEE' h
x : (Polynomial.map ιFE g).SplittingField
hx : eval₂ ιEE' x h = 0
hc : -(ιEE' γ - ιEE' (ιFE c) * x - ιEE' α) / (x - ιEE' β) ≠ (ιEE'.comp ιFE) c
⊢ x = ιEE' β
state_after: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
h_root : eval β h = 0
h_splits : Splits ιEE' h
x : (Polynomial.map ιFE g).SplittingField
hx : eval₂ ιEE' x h = 0
hc : -(ιEE' γ - ιEE' (ιFE c) * x - ιEE' α) / (x - ιEE' β) ≠ (ιEE'.comp ιFE) c
a : ¬x = ιEE' β
⊢ False

tactic: apply hc
state_before: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
h_root : eval β h = 0
h_splits : Splits ιEE' h
x : (Polynomial.map ιFE g).SplittingField
hx : eval₂ ιEE' x h = 0
hc : -(ιEE' γ - ιEE' (ιFE c) * x - ιEE' α) / (x - ιEE' β) ≠ (ιEE'.comp ιFE) c
a : ¬x = ιEE' β
⊢ False
state_after: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
h_root : eval β h = 0
h_splits : Splits ιEE' h
x : (Polynomial.map ιFE g).SplittingField
hx : eval₂ ιEE' x h = 0
hc : -(ιEE' γ - ιEE' (ιFE c) * x - ιEE' α) / (x - ιEE' β) ≠ (ιEE'.comp ιFE) c
a : ¬x = ιEE' β
⊢ -(ιEE' γ - ιEE' (ιFE c) * x - ιEE' α) / (x - ιEE' β) = (ιEE'.comp ιFE) c

tactic: apply (div_eq_iff (sub_ne_zero.mpr a)).mpr
state_before: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
h_root : eval β h = 0
h_splits : Splits ιEE' h
x : (Polynomial.map ιFE g).SplittingField
hx : eval₂ ιEE' x h = 0
hc : -(ιEE' γ - ιEE' (ιFE c) * x - ιEE' α) / (x - ιEE' β) ≠ (ιEE'.comp ιFE) c
a : ¬x = ιEE' β
⊢ -(ιEE' γ - ιEE' (ιFE c) * x - ιEE' α) / (x - ιEE' β) = (ιEE'.comp ιFE) c
state_after: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
h_root : eval β h = 0
h_splits : Splits ιEE' h
x : (Polynomial.map ιFE g).SplittingField
hx : eval₂ ιEE' x h = 0
hc : -(ιEE' γ - ιEE' (ιFE c) * x - ιEE' α) / (x - ιEE' β) ≠ (ιEE'.comp ιFE) c
a : ¬x = ιEE' β
⊢ -(ιEE' γ - ιEE' (ιFE c) * x - ιEE' α) = (ιEE'.comp ιFE) c * (x - ιEE' β)

tactic: simp only [γ, Algebra.smul_def, RingHom.map_add, RingHom.map_mul, RingHom.comp_apply]
state_before: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
h_root : eval β h = 0
h_splits : Splits ιEE' h
x : (Polynomial.map ιFE g).SplittingField
hx : eval₂ ιEE' x h = 0
hc : -(ιEE' γ - ιEE' (ιFE c) * x - ιEE' α) / (x - ιEE' β) ≠ (ιEE'.comp ιFE) c
a : ¬x = ιEE' β
⊢ -(ιEE' γ - ιEE' (ιFE c) * x - ιEE' α) = (ιEE'.comp ιFE) c * (x - ιEE' β)
state_after: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
h_root : eval β h = 0
h_splits : Splits ιEE' h
x : (Polynomial.map ιFE g).SplittingField
hx : eval₂ ιEE' x h = 0
hc : -(ιEE' γ - ιEE' (ιFE c) * x - ιEE' α) / (x - ιEE' β) ≠ (ιEE'.comp ιFE) c
a : ¬x = ιEE' β
⊢ -(ιEE' α + ιEE' ((algebraMap F E) c) * ιEE' β - ιEE' (ιFE c) * x - ιEE' α) = ιEE' (ιFE c) * (x - ιEE' β)

tactic: ring
state_before: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
h_root : eval β h = 0
h_splits : Splits ιEE' h
x : (Polynomial.map ιFE g).SplittingField
hx : eval₂ ιEE' x h = 0
hc : -(ιEE' γ - ιEE' (ιFE c) * x - ιEE' α) / (x - ιEE' β) ≠ (ιEE'.comp ιFE) c
a : ¬x = ιEE' β
⊢ -(ιEE' α + ιEE' ((algebraMap F E) c) * ιEE' β - ιEE' (ιFE c) * x - ιEE' α) = ιEE' (ιFE c) * (x - ιEE' β)
state_after: no goals

tactic: have f_root := root_left_of_root_gcd hx
state_before: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
h_root : eval β h = 0
h_splits : Splits ιEE' h
x : (Polynomial.map ιFE g).SplittingField
hx : eval₂ ιEE' x h = 0
⊢ ιEE' γ - ιEE' (ιFE c) * x ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots
state_after: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
h_root : eval β h = 0
h_splits : Splits ιEE' h
x : (Polynomial.map ιFE g).SplittingField
hx : eval₂ ιEE' x h = 0
f_root : eval₂ ιEE' x ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) = 0
⊢ ιEE' γ - ιEE' (ιFE c) * x ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots

tactic: rw [eval₂_comp, eval₂_sub, eval₂_mul, eval₂_C, eval₂_C, eval₂_X, eval₂_map] at f_root
state_before: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
h_root : eval β h = 0
h_splits : Splits ιEE' h
x : (Polynomial.map ιFE g).SplittingField
hx : eval₂ ιEE' x h = 0
f_root : eval₂ ιEE' x ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) = 0
⊢ ιEE' γ - ιEE' (ιFE c) * x ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots
state_after: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
h_root : eval β h = 0
h_splits : Splits ιEE' h
x : (Polynomial.map ιFE g).SplittingField
hx : eval₂ ιEE' x h = 0
f_root : eval₂ (ιEE'.comp ιFE) (ιEE' γ - ιEE' (ιFE c) * x) f = 0
⊢ ιEE' γ - ιEE' (ιFE c) * x ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots

tactic: exact (mem_roots_map (minpoly.ne_zero hα)).mpr f_root
state_before: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
h_root : eval β h = 0
h_splits : Splits ιEE' h
x : (Polynomial.map ιFE g).SplittingField
hx : eval₂ ιEE' x h = 0
f_root : eval₂ (ιEE'.comp ιFE) (ιEE' γ - ιEE' (ιFE c) * x) f = 0
⊢ ιEE' γ - ιEE' (ιFE c) * x ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots
state_after: no goals

tactic: rw [mem_roots_map (minpoly.ne_zero hβ), ← eval₂_map]
state_before: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
h_root : eval β h = 0
h_splits : Splits ιEE' h
x : (Polynomial.map ιFE g).SplittingField
hx : eval₂ ιEE' x h = 0
hc :
  ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots,
    -(ιEE' γ - ιEE' (ιFE c) * x - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
⊢ x ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots
state_after: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
h_root : eval β h = 0
h_splits : Splits ιEE' h
x : (Polynomial.map ιFE g).SplittingField
hx : eval₂ ιEE' x h = 0
hc :
  ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots,
    -(ιEE' γ - ιEE' (ιFE c) * x - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
⊢ eval₂ ιEE' x (Polynomial.map ιFE (minpoly F β)) = 0

tactic: exact root_right_of_root_gcd hx
state_before: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
h_root : eval β h = 0
h_splits : Splits ιEE' h
x : (Polynomial.map ιFE g).SplittingField
hx : eval₂ ιEE' x h = 0
hc :
  ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots,
    -(ιEE' γ - ιEE' (ιFE c) * x - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
⊢ eval₂ ιEE' x (Polynomial.map ιFE (minpoly F β)) = 0
state_after: no goals

tactic: dsimp only [γ]
state_before: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
h_root : eval β h = 0
h_splits : Splits ιEE' h
h_roots : ∀ x ∈ (Polynomial.map ιEE' h).roots, x = ιEE' β
⊢ Polynomial.map (algebraMap (↥F⟮γ⟯) E) p = EuclideanDomain.gcd ?intro.intro_1 ?intro.intro_2
state_after: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
h_root : eval β h = 0
h_splits : Splits ιEE' h
h_roots : ∀ x ∈ (Polynomial.map ιEE' h).roots, x = ιEE' β
⊢ Polynomial.map (algebraMap (↥F⟮α + c • β⟯) E) p = EuclideanDomain.gcd ?intro.intro_1 ?intro.intro_2

tactic: convert (gcd_map (algebraMap F⟮γ⟯ E)).symm
state_before: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
h_root : eval β h = 0
h_splits : Splits ιEE' h
h_roots : ∀ x ∈ (Polynomial.map ιEE' h).roots, x = ιEE' β
⊢ Polynomial.map (algebraMap (↥F⟮α + c • β⟯) E) p = EuclideanDomain.gcd ?intro.intro_1 ?intro.intro_2
state_after: no goals

tactic: simp only [map_comp, Polynomial.map_map, ← IsScalarTower.algebraMap_eq, Polynomial.map_sub,
  map_C, AdjoinSimple.algebraMap_gen, map_add, Polynomial.map_mul, map_X]
state_before: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
h_root : eval β h = 0
h_splits : Splits ιEE' h
h_roots : ∀ x ∈ (Polynomial.map ιEE' h).roots, x = ιEE' β
⊢ EuclideanDomain.gcd
      (Polynomial.map (algebraMap (↥F⟮γ⟯) E)
        ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X)))
      (Polynomial.map (algebraMap (↥F⟮γ⟯) E) (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)) =
    h
state_after: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
h_root : eval β h = 0
h_splits : Splits ιEE' h
h_roots : ∀ x ∈ (Polynomial.map ιEE' h).roots, x = ιEE' β
⊢ EuclideanDomain.gcd
      ((Polynomial.map (algebraMap F E) f).comp (C γ - C ((algebraMap (↥F⟮γ⟯) E) ⟨(algebraMap F E) c, ⋯⟩) * X))
      (Polynomial.map (algebraMap F E) g) =
    h

tactic: congr
state_before: F : Type u_1
inst✝⁴ : Field F
inst✝³ : Infinite F
E : Type u_2
inst✝² : Field E
ϕ : F →+* E
α β : E
inst✝¹ : Algebra F E
inst✝ : IsSeparable F E
hα : IsIntegral F α
hβ : IsIntegral F β
f : F[X] := minpoly F α
g : F[X] := minpoly F β
ιFE : F →+* E := algebraMap F E
ιEE' : E →+* (Polynomial.map ιFE g).SplittingField := algebraMap E (Polynomial.map ιFE g).SplittingField
c : F
hc :
  ∀ α' ∈ (Polynomial.map (ιEE'.comp ιFE) f).roots,
    ∀ β' ∈ (Polynomial.map (ιEE'.comp ιFE) g).roots, -(α' - ιEE' α) / (β' - ιEE' β) ≠ (ιEE'.comp ιFE) c
γ : E := α + c • β
p : (↥F⟮γ⟯)[X] :=
  EuclideanDomain.gcd
    ((Polynomial.map (algebraMap F ↥F⟮γ⟯) f).comp (C (AdjoinSimple.gen F γ) - C ⟨(algebraMap F E) c, ⋯⟩ * X))
    (Polynomial.map (algebraMap F ↥F⟮γ⟯) g)
h : E[X] := EuclideanDomain.gcd ((Polynomial.map ιFE f).comp (C γ - C (ιFE c) * X)) (Polynomial.map ιFE g)
map_g_ne_zero : Polynomial.map ιFE g ≠ 0
h_ne_zero : h ≠ 0
h_sep : h.Separable
h_root : eval β h = 0
h_splits : Splits ιEE' h
h_roots : ∀ x ∈ (Polynomial.map ιEE' h).roots, x = ιEE' β
⊢ EuclideanDomain.gcd
      ((Polynomial.map (algebraMap F E) f).comp (C γ - C ((algebraMap (↥F⟮γ⟯) E) ⟨(algebraMap F E) c, ⋯⟩) * X))
      (Polynomial.map (algebraMap F E) g) =
    h
state_after: no goals