-- Mathlib/Analysis/Complex/Polynomial/Basic.lean
theorem galActionHom_bijective_of_prime_degree {p : ℚ[X]} (p_irr : Irreducible p)
    (p_deg : p.natDegree.Prime)
    (p_roots : Fintype.card (p.rootSet ℂ) = Fintype.card (p.rootSet ℝ) + 2) :
    Function.Bijective (galActionHom p ℂ)

Proof state:
case h0
p : ℚ[X]
p_irr : Irreducible p
p_deg : Nat.Prime p.natDegree
p_roots : Fintype.card ↑(p.rootSet ℂ) = Fintype.card ↑(p.rootSet ℝ) + 2
h1 : Fintype.card ↑(p.rootSet ℂ) = p.natDegree
conj' : p.Gal := (restrict p ℂ) (AlgEquiv.restrictScalars ℚ conjAe)
x : Equiv.Perm ↑(p.rootSet ℂ)
⊢ Nat.Prime (Fintype.card ↑(p.rootSet ℂ))

Tactic:
rwa [h1]

Result:
no goals

Proof state:
p : ℚ[X]
p_irr : Irreducible p
p_deg : Nat.Prime p.natDegree
p_roots : Fintype.card ↑(p.rootSet ℂ) = Fintype.card ↑(p.rootSet ℝ) + 2
h1 : Fintype.card ↑(p.rootSet ℂ) = p.natDegree
⊢ Function.Bijective ⇑(galActionHom p ℂ)

Tactic:
let conj' := restrict p ℂ (Complex.conjAe.restrictScalars ℚ)

Result:
p : ℚ[X]
p_irr : Irreducible p
p_deg : Nat.Prime p.natDegree
p_roots : Fintype.card ↑(p.rootSet ℂ) = Fintype.card ↑(p.rootSet ℝ) + 2
h1 : Fintype.card ↑(p.rootSet ℂ) = p.natDegree
conj' : p.Gal := (restrict p ℂ) (AlgEquiv.restrictScalars ℚ conjAe)
⊢ Function.Bijective ⇑(galActionHom p ℂ)

Proof state:
case h3
p : ℚ[X]
p_irr : Irreducible p
p_deg : Nat.Prime p.natDegree
p_roots : Fintype.card ↑(p.rootSet ℂ) = Fintype.card ↑(p.rootSet ℝ) + 2
h1 : Fintype.card ↑(p.rootSet ℂ) = p.natDegree
conj' : p.Gal := (restrict p ℂ) (AlgEquiv.restrictScalars ℚ conjAe)
x : Equiv.Perm ↑(p.rootSet ℂ)
⊢ ((galActionHom p ℂ) conj').support.card = 2

Tactic:
apply Nat.add_left_cancel

Result:
case h3.a
p : ℚ[X]
p_irr : Irreducible p
p_deg : Nat.Prime p.natDegree
p_roots : Fintype.card ↑(p.rootSet ℂ) = Fintype.card ↑(p.rootSet ℝ) + 2
h1 : Fintype.card ↑(p.rootSet ℂ) = p.natDegree
conj' : p.Gal := (restrict p ℂ) (AlgEquiv.restrictScalars ℚ conjAe)
x : Equiv.Perm ↑(p.rootSet ℂ)
⊢ ?h3.n + ((galActionHom p ℂ) conj').support.card = ?h3.n + 2

case h3.n
p : ℚ[X]
p_irr : Irreducible p
p_deg : Nat.Prime p.natDegree
p_roots : Fintype.card ↑(p.rootSet ℂ) = Fintype.card ↑(p.rootSet ℝ) + 2
h1 : Fintype.card ↑(p.rootSet ℂ) = p.natDegree
conj' : p.Gal := (restrict p ℂ) (AlgEquiv.restrictScalars ℚ conjAe)
x : Equiv.Perm ↑(p.rootSet ℂ)
⊢ ℕ

Proof state:
p : ℚ[X]
p_irr : Irreducible p
p_deg : Nat.Prime p.natDegree
p_roots : Fintype.card ↑(p.rootSet ℂ) = Fintype.card ↑(p.rootSet ℝ) + 2
⊢ (p.aroots ℂ).toFinset.card = p.natDegree

Tactic:
rw [Multiset.toFinset_card_of_nodup, ← natDegree_eq_card_roots]

Result:
p : ℚ[X]
p_irr : Irreducible p
p_deg : Nat.Prime p.natDegree
p_roots : Fintype.card ↑(p.rootSet ℂ) = Fintype.card ↑(p.rootSet ℝ) + 2
⊢ Splits (algebraMap ℚ ℂ) p

p : ℚ[X]
p_irr : Irreducible p
p_deg : Nat.Prime p.natDegree
p_roots : Fintype.card ↑(p.rootSet ℂ) = Fintype.card ↑(p.rootSet ℝ) + 2
⊢ (p.aroots ℂ).Nodup

Proof state:
case h3.a
p : ℚ[X]
p_irr : Irreducible p
p_deg : Nat.Prime p.natDegree
p_roots : Fintype.card ↑(p.rootSet ℂ) = Fintype.card ↑(p.rootSet ℝ) + 2
h1 : Fintype.card ↑(p.rootSet ℂ) = p.natDegree
conj' : p.Gal := (restrict p ℂ) (AlgEquiv.restrictScalars ℚ conjAe)
x : Equiv.Perm ↑(p.rootSet ℂ)
⊢ (p.rootSet ℝ).toFinset.card + ((galActionHom p ℂ) conj').support.card = (p.rootSet ℂ).toFinset.card

Tactic:
exact (card_complex_roots_eq_card_real_add_card_not_gal_inv p).symm

Result:
no goals

Proof state:
case h3
p : ℚ[X]
p_irr : Irreducible p
p_deg : Nat.Prime p.natDegree
p_roots : Fintype.card ↑(p.rootSet ℂ) = Fintype.card ↑(p.rootSet ℝ) + 2
h1 : Fintype.card ↑(p.rootSet ℂ) = p.natDegree
conj' : p.Gal := (restrict p ℂ) (AlgEquiv.restrictScalars ℚ conjAe)
x : Equiv.Perm ↑(p.rootSet ℂ)
⊢ ((galActionHom p ℂ) conj').IsSwap

Tactic:
rw [← Equiv.Perm.card_support_eq_two]

Result:
case h3
p : ℚ[X]
p_irr : Irreducible p
p_deg : Nat.Prime p.natDegree
p_roots : Fintype.card ↑(p.rootSet ℂ) = Fintype.card ↑(p.rootSet ℝ) + 2
h1 : Fintype.card ↑(p.rootSet ℂ) = p.natDegree
conj' : p.Gal := (restrict p ℂ) (AlgEquiv.restrictScalars ℚ conjAe)
x : Equiv.Perm ↑(p.rootSet ℂ)
⊢ ((galActionHom p ℂ) conj').support.card = 2

Proof state:
case h2
p : ℚ[X]
p_irr : Irreducible p
p_deg : Nat.Prime p.natDegree
p_roots : Fintype.card ↑(p.rootSet ℂ) = Fintype.card ↑(p.rootSet ℝ) + 2
h1 : Fintype.card ↑(p.rootSet ℂ) = p.natDegree
conj' : p.Gal := (restrict p ℂ) (AlgEquiv.restrictScalars ℚ conjAe)
x : Equiv.Perm ↑(p.rootSet ℂ)
⊢ ?τ ∈ (galActionHom p ℂ).range

Tactic:
exact ⟨conj', rfl⟩

Result:
no goals

Proof state:
p : ℚ[X]
p_irr : Irreducible p
p_deg : Nat.Prime p.natDegree
p_roots : Fintype.card ↑(p.rootSet ℂ) = Fintype.card ↑(p.rootSet ℝ) + 2
⊢ (p.aroots ℂ).Nodup

Tactic:
exact nodup_roots ((separable_map (algebraMap ℚ ℂ)).mpr p_irr.separable)

Result:
no goals

Proof state:
p : ℚ[X]
p_irr : Irreducible p
p_deg : Nat.Prime p.natDegree
p_roots : Fintype.card ↑(p.rootSet ℂ) = Fintype.card ↑(p.rootSet ℝ) + 2
⊢ Splits (algebraMap ℚ ℂ) p

Tactic:
exact IsAlgClosed.splits_codomain p

Result:
no goals

Proof state:
case h3.a
p : ℚ[X]
p_irr : Irreducible p
p_deg : Nat.Prime p.natDegree
p_roots : Fintype.card ↑(p.rootSet ℂ) = Fintype.card ↑(p.rootSet ℝ) + 2
h1 : Fintype.card ↑(p.rootSet ℂ) = p.natDegree
conj' : p.Gal := (restrict p ℂ) (AlgEquiv.restrictScalars ℚ conjAe)
x : Equiv.Perm ↑(p.rootSet ℂ)
⊢ ?h3.n + ((galActionHom p ℂ) conj').support.card = ?h3.n + 2

case h3.n
p : ℚ[X]
p_irr : Irreducible p
p_deg : Nat.Prime p.natDegree
p_roots : Fintype.card ↑(p.rootSet ℂ) = Fintype.card ↑(p.rootSet ℝ) + 2
h1 : Fintype.card ↑(p.rootSet ℂ) = p.natDegree
conj' : p.Gal := (restrict p ℂ) (AlgEquiv.restrictScalars ℚ conjAe)
x : Equiv.Perm ↑(p.rootSet ℂ)
⊢ ℕ

Tactic:
rw [← p_roots, ← Set.toFinset_card (rootSet p ℝ), ← Set.toFinset_card (rootSet p ℂ)]

Result:
case h3.a
p : ℚ[X]
p_irr : Irreducible p
p_deg : Nat.Prime p.natDegree
p_roots : Fintype.card ↑(p.rootSet ℂ) = Fintype.card ↑(p.rootSet ℝ) + 2
h1 : Fintype.card ↑(p.rootSet ℂ) = p.natDegree
conj' : p.Gal := (restrict p ℂ) (AlgEquiv.restrictScalars ℚ conjAe)
x : Equiv.Perm ↑(p.rootSet ℂ)
⊢ (p.rootSet ℝ).toFinset.card + ((galActionHom p ℂ) conj').support.card = (p.rootSet ℂ).toFinset.card