Theorem: Polynomial.cyclotomic_mul_prime_eq_pow_of_not_dvd
File: Mathlib/RingTheory/Polynomial/Cyclotomic/Expand.lean

Proof steps:
state_before: R : Type u_1
p n : ℕ
hp : Fact (Nat.Prime p)
inst✝¹ : Ring R
inst✝ : CharP R p
hn : ¬p ∣ n
⊢ cyclotomic (n * p) R = cyclotomic n R ^ (p - 1)
state_after: R : Type u_1
p n : ℕ
hp : Fact (Nat.Prime p)
inst✝¹ : Ring R
inst✝ : CharP R p
hn : ¬p ∣ n
this : Algebra (ZMod p) R := ZMod.algebra R p
⊢ cyclotomic (n * p) R = cyclotomic n R ^ (p - 1)
tactic: letI : Algebra (ZMod p) R := ZMod.algebra _ _
state_before: R : Type u_1
p n : ℕ
hp : Fact (Nat.Prime p)
inst✝¹ : Ring R
inst✝ : CharP R p
hn : ¬p ∣ n
this : Algebra (ZMod p) R := ZMod.algebra R p
⊢ cyclotomic (n * p) R = cyclotomic n R ^ (p - 1)
state_after: R : Type u_1
p n : ℕ
hp : Fact (Nat.Prime p)
inst✝¹ : Ring R
inst✝ : CharP R p
hn : ¬p ∣ n
this : Algebra (ZMod p) R := ZMod.algebra R p
⊢ cyclotomic (n * p) (ZMod p) = cyclotomic n (ZMod p) ^ (p - 1)
tactic: suffices cyclotomic (n * p) (ZMod p) = cyclotomic n (ZMod p) ^ (p - 1) by
    rw [← map_cyclotomic _ (algebraMap (ZMod p) R), ← map_cyclotomic _ (algebraMap (ZMod p) R),
      this, Polynomial.map_pow]
state_before: R : Type u_1
p n : ℕ
hp : Fact (Nat.Prime p)
inst✝¹ : Ring R
inst✝ : CharP R p
hn : ¬p ∣ n
this : Algebra (ZMod p) R := ZMod.algebra R p
⊢ cyclotomic (n * p) (ZMod p) = cyclotomic n (ZMod p) ^ (p - 1)
state_after: case a
R : Type u_1
p n : ℕ
hp : Fact (Nat.Prime p)
inst✝¹ : Ring R
inst✝ : CharP R p
hn : ¬p ∣ n
this : Algebra (ZMod p) R := ZMod.algebra R p
⊢ (fun x => cyclotomic n (ZMod p) * x) (cyclotomic (n * p) (ZMod p)) =
    (fun x => cyclotomic n (ZMod p) * x) (cyclotomic n (ZMod p) ^ (p - 1))
tactic: apply mul_right_injective₀ (cyclotomic_ne_zero n <| ZMod p)
state_before: case a
R : Type u_1
p n : ℕ
hp : Fact (Nat.Prime p)
inst✝¹ : Ring R
inst✝ : CharP R p
hn : ¬p ∣ n
this : Algebra (ZMod p) R := ZMod.algebra R p
⊢ (fun x => cyclotomic n (ZMod p) * x) (cyclotomic (n * p) (ZMod p)) =
    (fun x => cyclotomic n (ZMod p) * x) (cyclotomic n (ZMod p) ^ (p - 1))
state_after: case a
R : Type u_1
p n : ℕ
hp : Fact (Nat.Prime p)
inst✝¹ : Ring R
inst✝ : CharP R p
hn : ¬p ∣ n
this : Algebra (ZMod p) R := ZMod.algebra R p
⊢ cyclotomic n (ZMod p) * cyclotomic (n * p) (ZMod p) = cyclotomic n (ZMod p) * cyclotomic n (ZMod p) ^ (p - 1)
tactic: dsimp
state_before: case a
R : Type u_1
p n : ℕ
hp : Fact (Nat.Prime p)
inst✝¹ : Ring R
inst✝ : CharP R p
hn : ¬p ∣ n
this : Algebra (ZMod p) R := ZMod.algebra R p
⊢ cyclotomic n (ZMod p) * cyclotomic (n * p) (ZMod p) = cyclotomic n (ZMod p) * cyclotomic n (ZMod p) ^ (p - 1)
state_after: case a
R : Type u_1
p n : ℕ
hp : Fact (Nat.Prime p)
inst✝¹ : Ring R
inst✝ : CharP R p
hn : ¬p ∣ n
this : Algebra (ZMod p) R := ZMod.algebra R p
⊢ cyclotomic (n * p) (ZMod p) * cyclotomic n (ZMod p) = (expand (ZMod p) p) (cyclotomic n (ZMod p))
tactic: rw [← pow_succ', tsub_add_cancel_of_le hp.out.one_lt.le, mul_comm, ← ZMod.expand_card]
state_before: case a
R : Type u_1
p n : ℕ
hp : Fact (Nat.Prime p)
inst✝¹ : Ring R
inst✝ : CharP R p
hn : ¬p ∣ n
this : Algebra (ZMod p) R := ZMod.algebra R p
⊢ cyclotomic (n * p) (ZMod p) * cyclotomic n (ZMod p) = (expand (ZMod p) p) (cyclotomic n (ZMod p))
state_after: case a
R : Type u_1
p n : ℕ
hp : Fact (Nat.Prime p)
inst✝¹ : Ring R
inst✝ : CharP R p
hn : ¬p ∣ n
this : Algebra (ZMod p) R := ZMod.algebra R p
⊢ cyclotomic (n * p) (ZMod p) * cyclotomic n (ZMod p) =
    (expand (ZMod p) p) (map (Int.castRingHom (ZMod p)) (cyclotomic n ℤ))
tactic: conv_rhs => rw [← map_cyclotomic_int]
state_before: case a
R : Type u_1
p n : ℕ
hp : Fact (Nat.Prime p)
inst✝¹ : Ring R
inst✝ : CharP R p
hn : ¬p ∣ n
this : Algebra (ZMod p) R := ZMod.algebra R p
⊢ cyclotomic (n * p) (ZMod p) * cyclotomic n (ZMod p) =
    (expand (ZMod p) p) (map (Int.castRingHom (ZMod p)) (cyclotomic n ℤ))
state_after: no goals
tactic: rw [← map_expand, cyclotomic_expand_eq_cyclotomic_mul hp.out hn, Polynomial.map_mul,
    map_cyclotomic, map_cyclotomic]