Theorem: gal_X_pow_sub_C_isSolvable_aux
File: Mathlib/FieldTheory/AbelRuffini.lean

Proof steps:
state_before: F : Type u_1
inst✝² : Field F
E : Type u_2
inst✝¹ : Field E
inst✝ : Algebra F E
n : ℕ
a : F
h : Splits (RingHom.id F) (X ^ n - 1)
⊢ IsSolvable (X ^ n - C a).Gal
state_after: case pos
F : Type u_1
inst✝² : Field F
E : Type u_2
inst✝¹ : Field E
inst✝ : Algebra F E
n : ℕ
a : F
h : Splits (RingHom.id F) (X ^ n - 1)
ha : a = 0
⊢ IsSolvable (X ^ n - C a).Gal

case neg
F : Type u_1
inst✝² : Field F
E : Type u_2
inst✝¹ : Field E
inst✝ : Algebra F E
n : ℕ
a : F
h : Splits (RingHom.id F) (X ^ n - 1)
ha : ¬a = 0
⊢ IsSolvable (X ^ n - C a).Gal
tactic: by_cases ha : a = 0
state_before: case neg
F : Type u_1
inst✝² : Field F
E : Type u_2
inst✝¹ : Field E
inst✝ : Algebra F E
n : ℕ
a : F
h : Splits (RingHom.id F) (X ^ n - 1)
ha : ¬a = 0
⊢ IsSolvable (X ^ n - C a).Gal
state_after: case neg
F : Type u_1
inst✝² : Field F
E : Type u_2
inst✝¹ : Field E
inst✝ : Algebra F E
n : ℕ
a : F
h : Splits (RingHom.id F) (X ^ n - 1)
ha : ¬a = 0
ha' : (algebraMap F (X ^ n - C a).SplittingField) a ≠ 0
⊢ IsSolvable (X ^ n - C a).Gal
tactic: have ha' : algebraMap F (X ^ n - C a).SplittingField a ≠ 0 :=
    mt ((injective_iff_map_eq_zero _).mp (RingHom.injective _) a) ha
state_before: case neg
F : Type u_1
inst✝² : Field F
E : Type u_2
inst✝¹ : Field E
inst✝ : Algebra F E
n : ℕ
a : F
h : Splits (RingHom.id F) (X ^ n - 1)
ha : ¬a = 0
ha' : (algebraMap F (X ^ n - C a).SplittingField) a ≠ 0
⊢ IsSolvable (X ^ n - C a).Gal
state_after: case pos
F : Type u_1
inst✝² : Field F
E : Type u_2
inst✝¹ : Field E
inst✝ : Algebra F E
n : ℕ
a : F
h : Splits (RingHom.id F) (X ^ n - 1)
ha : ¬a = 0
ha' : (algebraMap F (X ^ n - C a).SplittingField) a ≠ 0
hn : n = 0
⊢ IsSolvable (X ^ n - C a).Gal

case neg
F : Type u_1
inst✝² : Field F
E : Type u_2
inst✝¹ : Field E
inst✝ : Algebra F E
n : ℕ
a : F
h : Splits (RingHom.id F) (X ^ n - 1)
ha : ¬a = 0
ha' : (algebraMap F (X ^ n - C a).SplittingField) a ≠ 0
hn : ¬n = 0
⊢ IsSolvable (X ^ n - C a).Gal
tactic: by_cases hn : n = 0
state_before: case neg
F : Type u_1
inst✝² : Field F
E : Type u_2
inst✝¹ : Field E
inst✝ : Algebra F E
n : ℕ
a : F
h : Splits (RingHom.id F) (X ^ n - 1)
ha : ¬a = 0
ha' : (algebraMap F (X ^ n - C a).SplittingField) a ≠ 0
hn : ¬n = 0
⊢ IsSolvable (X ^ n - C a).Gal
state_after: case neg
F : Type u_1
inst✝² : Field F
E : Type u_2
inst✝¹ : Field E
inst✝ : Algebra F E
n : ℕ
a : F
h : Splits (RingHom.id F) (X ^ n - 1)
ha : ¬a = 0
ha' : (algebraMap F (X ^ n - C a).SplittingField) a ≠ 0
hn : ¬n = 0
hn' : 0 < n
⊢ IsSolvable (X ^ n - C a).Gal
tactic: have hn' : 0 < n := pos_iff_ne_zero.mpr hn
state_before: case neg
F : Type u_1
inst✝² : Field F
E : Type u_2
inst✝¹ : Field E
inst✝ : Algebra F E
n : ℕ
a : F
h : Splits (RingHom.id F) (X ^ n - 1)
ha : ¬a = 0
ha' : (algebraMap F (X ^ n - C a).SplittingField) a ≠ 0
hn : ¬n = 0
hn' : 0 < n
⊢ IsSolvable (X ^ n - C a).Gal
state_after: case neg
F : Type u_1
inst✝² : Field F
E : Type u_2
inst✝¹ : Field E
inst✝ : Algebra F E
n : ℕ
a : F
h : Splits (RingHom.id F) (X ^ n - 1)
ha : ¬a = 0
ha' : (algebraMap F (X ^ n - C a).SplittingField) a ≠ 0
hn : ¬n = 0
hn' : 0 < n
hn'' : X ^ n - C a ≠ 0
⊢ IsSolvable (X ^ n - C a).Gal
tactic: have hn'' : X ^ n - C a ≠ 0 := X_pow_sub_C_ne_zero hn' a
state_before: case neg
F : Type u_1
inst✝² : Field F
E : Type u_2
inst✝¹ : Field E
inst✝ : Algebra F E
n : ℕ
a : F
h : Splits (RingHom.id F) (X ^ n - 1)
ha : ¬a = 0
ha' : (algebraMap F (X ^ n - C a).SplittingField) a ≠ 0
hn : ¬n = 0
hn' : 0 < n
hn'' : X ^ n - C a ≠ 0
⊢ IsSolvable (X ^ n - C a).Gal
state_after: case neg
F : Type u_1
inst✝² : Field F
E : Type u_2
inst✝¹ : Field E
inst✝ : Algebra F E
n : ℕ
a : F
h : Splits (RingHom.id F) (X ^ n - 1)
ha : ¬a = 0
ha' : (algebraMap F (X ^ n - C a).SplittingField) a ≠ 0
hn : ¬n = 0
hn' : 0 < n
hn'' : X ^ n - C a ≠ 0
hn''' : X ^ n - 1 ≠ 0
⊢ IsSolvable (X ^ n - C a).Gal
tactic: have hn''' : (X ^ n - 1 : F[X]) ≠ 0 := X_pow_sub_C_ne_zero hn' 1
state_before: case neg
F : Type u_1
inst✝² : Field F
E : Type u_2
inst✝¹ : Field E
inst✝ : Algebra F E
n : ℕ
a : F
h : Splits (RingHom.id F) (X ^ n - 1)
ha : ¬a = 0
ha' : (algebraMap F (X ^ n - C a).SplittingField) a ≠ 0
hn : ¬n = 0
hn' : 0 < n
hn'' : X ^ n - C a ≠ 0
hn''' : X ^ n - 1 ≠ 0
⊢ IsSolvable (X ^ n - C a).Gal
state_after: case neg
F : Type u_1
inst✝² : Field F
E : Type u_2
inst✝¹ : Field E
inst✝ : Algebra F E
n : ℕ
a : F
h : Splits (RingHom.id F) (X ^ n - 1)
ha : ¬a = 0
ha' : (algebraMap F (X ^ n - C a).SplittingField) a ≠ 0
hn : ¬n = 0
hn' : 0 < n
hn'' : X ^ n - C a ≠ 0
hn''' : X ^ n - 1 ≠ 0
mem_range : ∀ {c : (X ^ n - C a).SplittingField}, c ^ n = 1 → ∃ d, (algebraMap F (X ^ n - C a).SplittingField) d = c
⊢ IsSolvable (X ^ n - C a).Gal
tactic: have mem_range : ∀ {c : (X ^ n - C a).SplittingField},
      (c ^ n = 1 → (∃ d, algebraMap F (X ^ n - C a).SplittingField d = c)) := fun {c} hc =>
    RingHom.mem_range.mp (minpoly.mem_range_of_degree_eq_one F c (h.def.resolve_left hn'''
      (minpoly.irreducible ((SplittingField.instNormal (X ^ n - C a)).isIntegral c))
      (minpoly.dvd F c (by rwa [map_id, map_sub, sub_eq_zero, aeval_X_pow, aeval_one]))))
state_before: case neg
F : Type u_1
inst✝² : Field F
E : Type u_2
inst✝¹ : Field E
inst✝ : Algebra F E
n : ℕ
a : F
h : Splits (RingHom.id F) (X ^ n - 1)
ha : ¬a = 0
ha' : (algebraMap F (X ^ n - C a).SplittingField) a ≠ 0
hn : ¬n = 0
hn' : 0 < n
hn'' : X ^ n - C a ≠ 0
hn''' : X ^ n - 1 ≠ 0
mem_range : ∀ {c : (X ^ n - C a).SplittingField}, c ^ n = 1 → ∃ d, (algebraMap F (X ^ n - C a).SplittingField) d = c
⊢ IsSolvable (X ^ n - C a).Gal
state_after: case neg.h
F : Type u_1
inst✝² : Field F
E : Type u_2
inst✝¹ : Field E
inst✝ : Algebra F E
n : ℕ
a : F
h : Splits (RingHom.id F) (X ^ n - 1)
ha : ¬a = 0
ha' : (algebraMap F (X ^ n - C a).SplittingField) a ≠ 0
hn : ¬n = 0
hn' : 0 < n
hn'' : X ^ n - C a ≠ 0
hn''' : X ^ n - 1 ≠ 0
mem_range : ∀ {c : (X ^ n - C a).SplittingField}, c ^ n = 1 → ∃ d, (algebraMap F (X ^ n - C a).SplittingField) d = c
⊢ ∀ (a_1 b : (X ^ n - C a).Gal), a_1 * b = b * a_1
tactic: apply isSolvable_of_comm
state_before: case neg.h
F : Type u_1
inst✝² : Field F
E : Type u_2
inst✝¹ : Field E
inst✝ : Algebra F E
n : ℕ
a : F
h : Splits (RingHom.id F) (X ^ n - 1)
ha : ¬a = 0
ha' : (algebraMap F (X ^ n - C a).SplittingField) a ≠ 0
hn : ¬n = 0
hn' : 0 < n
hn'' : X ^ n - C a ≠ 0
hn''' : X ^ n - 1 ≠ 0
mem_range : ∀ {c : (X ^ n - C a).SplittingField}, c ^ n = 1 → ∃ d, (algebraMap F (X ^ n - C a).SplittingField) d = c
⊢ ∀ (a_1 b : (X ^ n - C a).Gal), a_1 * b = b * a_1
state_after: case neg.h
F : Type u_1
inst✝² : Field F
E : Type u_2
inst✝¹ : Field E
inst✝ : Algebra F E
n : ℕ
a : F
h : Splits (RingHom.id F) (X ^ n - 1)
ha : ¬a = 0
ha' : (algebraMap F (X ^ n - C a).SplittingField) a ≠ 0
hn : ¬n = 0
hn' : 0 < n
hn'' : X ^ n - C a ≠ 0
hn''' : X ^ n - 1 ≠ 0
mem_range : ∀ {c : (X ^ n - C a).SplittingField}, c ^ n = 1 → ∃ d, (algebraMap F (X ^ n - C a).SplittingField) d = c
σ τ : (X ^ n - C a).Gal
⊢ σ * τ = τ * σ
tactic: intro σ τ
state_before: case neg.h
F : Type u_1
inst✝² : Field F
E : Type u_2
inst✝¹ : Field E
inst✝ : Algebra F E
n : ℕ
a : F
h : Splits (RingHom.id F) (X ^ n - 1)
ha : ¬a = 0
ha' : (algebraMap F (X ^ n - C a).SplittingField) a ≠ 0
hn : ¬n = 0
hn' : 0 < n
hn'' : X ^ n - C a ≠ 0
hn''' : X ^ n - 1 ≠ 0
mem_range : ∀ {c : (X ^ n - C a).SplittingField}, c ^ n = 1 → ∃ d, (algebraMap F (X ^ n - C a).SplittingField) d = c
σ τ : (X ^ n - C a).Gal
⊢ σ * τ = τ * σ
state_after: case neg.h.h
F : Type u_1
inst✝² : Field F
E : Type u_2
inst✝¹ : Field E
inst✝ : Algebra F E
n : ℕ
a : F
h : Splits (RingHom.id F) (X ^ n - 1)
ha : ¬a = 0
ha' : (algebraMap F (X ^ n - C a).SplittingField) a ≠ 0
hn : ¬n = 0
hn' : 0 < n
hn'' : X ^ n - C a ≠ 0
hn''' : X ^ n - 1 ≠ 0
mem_range : ∀ {c : (X ^ n - C a).SplittingField}, c ^ n = 1 → ∃ d, (algebraMap F (X ^ n - C a).SplittingField) d = c
σ τ : (X ^ n - C a).Gal
b : (X ^ n - C a).SplittingField
hb : b ∈ (X ^ n - C a).rootSet (X ^ n - C a).SplittingField
⊢ (σ * τ) b = (τ * σ) b
tactic: ext b hb
state_before: case neg.h.h
F : Type u_1
inst✝² : Field F
E : Type u_2
inst✝¹ : Field E
inst✝ : Algebra F E
n : ℕ
a : F
h : Splits (RingHom.id F) (X ^ n - 1)
ha : ¬a = 0
ha' : (algebraMap F (X ^ n - C a).SplittingField) a ≠ 0
hn : ¬n = 0
hn' : 0 < n
hn'' : X ^ n - C a ≠ 0
hn''' : X ^ n - 1 ≠ 0
mem_range : ∀ {c : (X ^ n - C a).SplittingField}, c ^ n = 1 → ∃ d, (algebraMap F (X ^ n - C a).SplittingField) d = c
σ τ : (X ^ n - C a).Gal
b : (X ^ n - C a).SplittingField
hb : b ∈ (X ^ n - C a).rootSet (X ^ n - C a).SplittingField
⊢ (σ * τ) b = (τ * σ) b
state_after: case neg.h.h
F : Type u_1
inst✝² : Field F
E : Type u_2
inst✝¹ : Field E
inst✝ : Algebra F E
n : ℕ
a : F
h : Splits (RingHom.id F) (X ^ n - 1)
ha : ¬a = 0
ha' : (algebraMap F (X ^ n - C a).SplittingField) a ≠ 0
hn : ¬n = 0
hn' : 0 < n
hn'' : X ^ n - C a ≠ 0
hn''' : X ^ n - 1 ≠ 0
mem_range : ∀ {c : (X ^ n - C a).SplittingField}, c ^ n = 1 → ∃ d, (algebraMap F (X ^ n - C a).SplittingField) d = c
σ τ : (X ^ n - C a).Gal
b : (X ^ n - C a).SplittingField
hb : b ^ n = (algebraMap F (X ^ n - C a).SplittingField) a
⊢ (σ * τ) b = (τ * σ) b
tactic: rw [mem_rootSet_of_ne hn'', map_sub, aeval_X_pow, aeval_C, sub_eq_zero] at hb
state_before: case neg.h.h
F : Type u_1
inst✝² : Field F
E : Type u_2
inst✝¹ : Field E
inst✝ : Algebra F E
n : ℕ
a : F
h : Splits (RingHom.id F) (X ^ n - 1)
ha : ¬a = 0
ha' : (algebraMap F (X ^ n - C a).SplittingField) a ≠ 0
hn : ¬n = 0
hn' : 0 < n
hn'' : X ^ n - C a ≠ 0
hn''' : X ^ n - 1 ≠ 0
mem_range : ∀ {c : (X ^ n - C a).SplittingField}, c ^ n = 1 → ∃ d, (algebraMap F (X ^ n - C a).SplittingField) d = c
σ τ : (X ^ n - C a).Gal
b : (X ^ n - C a).SplittingField
hb : b ^ n = (algebraMap F (X ^ n - C a).SplittingField) a
⊢ (σ * τ) b = (τ * σ) b
state_after: case neg.h.h
F : Type u_1
inst✝² : Field F
E : Type u_2
inst✝¹ : Field E
inst✝ : Algebra F E
n : ℕ
a : F
h : Splits (RingHom.id F) (X ^ n - 1)
ha : ¬a = 0
ha' : (algebraMap F (X ^ n - C a).SplittingField) a ≠ 0
hn : ¬n = 0
hn' : 0 < n
hn'' : X ^ n - C a ≠ 0
hn''' : X ^ n - 1 ≠ 0
mem_range : ∀ {c : (X ^ n - C a).SplittingField}, c ^ n = 1 → ∃ d, (algebraMap F (X ^ n - C a).SplittingField) d = c
σ τ : (X ^ n - C a).Gal
b : (X ^ n - C a).SplittingField
hb : b ^ n = (algebraMap F (X ^ n - C a).SplittingField) a
hb' : b ≠ 0
⊢ (σ * τ) b = (τ * σ) b
tactic: have hb' : b ≠ 0 := by
    intro hb'
    rw [hb', zero_pow hn] at hb
    exact ha' hb.symm
state_before: case neg.h.h
F : Type u_1
inst✝² : Field F
E : Type u_2
inst✝¹ : Field E
inst✝ : Algebra F E
n : ℕ
a : F
h : Splits (RingHom.id F) (X ^ n - 1)
ha : ¬a = 0
ha' : (algebraMap F (X ^ n - C a).SplittingField) a ≠ 0
hn : ¬n = 0
hn' : 0 < n
hn'' : X ^ n - C a ≠ 0
hn''' : X ^ n - 1 ≠ 0
mem_range : ∀ {c : (X ^ n - C a).SplittingField}, c ^ n = 1 → ∃ d, (algebraMap F (X ^ n - C a).SplittingField) d = c
σ τ : (X ^ n - C a).Gal
b : (X ^ n - C a).SplittingField
hb : b ^ n = (algebraMap F (X ^ n - C a).SplittingField) a
hb' : b ≠ 0
⊢ (σ * τ) b = (τ * σ) b
state_after: case neg.h.h
F : Type u_1
inst✝² : Field F
E : Type u_2
inst✝¹ : Field E
inst✝ : Algebra F E
n : ℕ
a : F
h : Splits (RingHom.id F) (X ^ n - 1)
ha : ¬a = 0
ha' : (algebraMap F (X ^ n - C a).SplittingField) a ≠ 0
hn : ¬n = 0
hn' : 0 < n
hn'' : X ^ n - C a ≠ 0
hn''' : X ^ n - 1 ≠ 0
mem_range : ∀ {c : (X ^ n - C a).SplittingField}, c ^ n = 1 → ∃ d, (algebraMap F (X ^ n - C a).SplittingField) d = c
σ τ : (X ^ n - C a).Gal
b : (X ^ n - C a).SplittingField
hb : b ^ n = (algebraMap F (X ^ n - C a).SplittingField) a
hb' : b ≠ 0
key : ∀ (σ : (X ^ n - C a).Gal), ∃ c, σ b = b * (algebraMap F (X ^ n - C a).SplittingField) c
⊢ (σ * τ) b = (τ * σ) b
tactic: have key : ∀ σ : (X ^ n - C a).Gal, ∃ c, σ b = b * algebraMap F _ c := by
    intro σ
    have key : (σ b / b) ^ n = 1 := by rw [div_pow, ← map_pow, hb, σ.commutes, div_self ha']
    obtain ⟨c, hc⟩ := mem_range key
    use c
    rw [hc, mul_div_cancel₀ (σ b) hb']
state_before: case neg.h.h
F : Type u_1
inst✝² : Field F
E : Type u_2
inst✝¹ : Field E
inst✝ : Algebra F E
n : ℕ
a : F
h : Splits (RingHom.id F) (X ^ n - 1)
ha : ¬a = 0
ha' : (algebraMap F (X ^ n - C a).SplittingField) a ≠ 0
hn : ¬n = 0
hn' : 0 < n
hn'' : X ^ n - C a ≠ 0
hn''' : X ^ n - 1 ≠ 0
mem_range : ∀ {c : (X ^ n - C a).SplittingField}, c ^ n = 1 → ∃ d, (algebraMap F (X ^ n - C a).SplittingField) d = c
σ τ : (X ^ n - C a).Gal
b : (X ^ n - C a).SplittingField
hb : b ^ n = (algebraMap F (X ^ n - C a).SplittingField) a
hb' : b ≠ 0
key : ∀ (σ : (X ^ n - C a).Gal), ∃ c, σ b = b * (algebraMap F (X ^ n - C a).SplittingField) c
⊢ (σ * τ) b = (τ * σ) b
state_after: case neg.h.h.intro
F : Type u_1
inst✝² : Field F
E : Type u_2
inst✝¹ : Field E
inst✝ : Algebra F E
n : ℕ
a : F
h : Splits (RingHom.id F) (X ^ n - 1)
ha : ¬a = 0
ha' : (algebraMap F (X ^ n - C a).SplittingField) a ≠ 0
hn : ¬n = 0
hn' : 0 < n
hn'' : X ^ n - C a ≠ 0
hn''' : X ^ n - 1 ≠ 0
mem_range : ∀ {c : (X ^ n - C a).SplittingField}, c ^ n = 1 → ∃ d, (algebraMap F (X ^ n - C a).SplittingField) d = c
σ τ : (X ^ n - C a).Gal
b : (X ^ n - C a).SplittingField
hb : b ^ n = (algebraMap F (X ^ n - C a).SplittingField) a
hb' : b ≠ 0
key : ∀ (σ : (X ^ n - C a).Gal), ∃ c, σ b = b * (algebraMap F (X ^ n - C a).SplittingField) c
c : F
hc : σ b = b * (algebraMap F (X ^ n - C a).SplittingField) c
⊢ (σ * τ) b = (τ * σ) b
tactic: obtain ⟨c, hc⟩ := key σ
state_before: case neg.h.h.intro
F : Type u_1
inst✝² : Field F
E : Type u_2
inst✝¹ : Field E
inst✝ : Algebra F E
n : ℕ
a : F
h : Splits (RingHom.id F) (X ^ n - 1)
ha : ¬a = 0
ha' : (algebraMap F (X ^ n - C a).SplittingField) a ≠ 0
hn : ¬n = 0
hn' : 0 < n
hn'' : X ^ n - C a ≠ 0
hn''' : X ^ n - 1 ≠ 0
mem_range : ∀ {c : (X ^ n - C a).SplittingField}, c ^ n = 1 → ∃ d, (algebraMap F (X ^ n - C a).SplittingField) d = c
σ τ : (X ^ n - C a).Gal
b : (X ^ n - C a).SplittingField
hb : b ^ n = (algebraMap F (X ^ n - C a).SplittingField) a
hb' : b ≠ 0
key : ∀ (σ : (X ^ n - C a).Gal), ∃ c, σ b = b * (algebraMap F (X ^ n - C a).SplittingField) c
c : F
hc : σ b = b * (algebraMap F (X ^ n - C a).SplittingField) c
⊢ (σ * τ) b = (τ * σ) b
state_after: case neg.h.h.intro.intro
F : Type u_1
inst✝² : Field F
E : Type u_2
inst✝¹ : Field E
inst✝ : Algebra F E
n : ℕ
a : F
h : Splits (RingHom.id F) (X ^ n - 1)
ha : ¬a = 0
ha' : (algebraMap F (X ^ n - C a).SplittingField) a ≠ 0
hn : ¬n = 0
hn' : 0 < n
hn'' : X ^ n - C a ≠ 0
hn''' : X ^ n - 1 ≠ 0
mem_range : ∀ {c : (X ^ n - C a).SplittingField}, c ^ n = 1 → ∃ d, (algebraMap F (X ^ n - C a).SplittingField) d = c
σ τ : (X ^ n - C a).Gal
b : (X ^ n - C a).SplittingField
hb : b ^ n = (algebraMap F (X ^ n - C a).SplittingField) a
hb' : b ≠ 0
key : ∀ (σ : (X ^ n - C a).Gal), ∃ c, σ b = b * (algebraMap F (X ^ n - C a).SplittingField) c
c : F
hc : σ b = b * (algebraMap F (X ^ n - C a).SplittingField) c
d : F
hd : τ b = b * (algebraMap F (X ^ n - C a).SplittingField) d
⊢ (σ * τ) b = (τ * σ) b
tactic: obtain ⟨d, hd⟩ := key τ
state_before: case neg.h.h.intro.intro
F : Type u_1
inst✝² : Field F
E : Type u_2
inst✝¹ : Field E
inst✝ : Algebra F E
n : ℕ
a : F
h : Splits (RingHom.id F) (X ^ n - 1)
ha : ¬a = 0
ha' : (algebraMap F (X ^ n - C a).SplittingField) a ≠ 0
hn : ¬n = 0
hn' : 0 < n
hn'' : X ^ n - C a ≠ 0
hn''' : X ^ n - 1 ≠ 0
mem_range : ∀ {c : (X ^ n - C a).SplittingField}, c ^ n = 1 → ∃ d, (algebraMap F (X ^ n - C a).SplittingField) d = c
σ τ : (X ^ n - C a).Gal
b : (X ^ n - C a).SplittingField
hb : b ^ n = (algebraMap F (X ^ n - C a).SplittingField) a
hb' : b ≠ 0
key : ∀ (σ : (X ^ n - C a).Gal), ∃ c, σ b = b * (algebraMap F (X ^ n - C a).SplittingField) c
c : F
hc : σ b = b * (algebraMap F (X ^ n - C a).SplittingField) c
d : F
hd : τ b = b * (algebraMap F (X ^ n - C a).SplittingField) d
⊢ (σ * τ) b = (τ * σ) b
state_after: no goals
tactic: rw [σ.mul_apply, τ.mul_apply, hc, map_mul, τ.commutes, hd, map_mul, σ.commutes, hc,
    mul_assoc, mul_assoc, mul_right_inj' hb', mul_comm]