Binomial irreducibility and finite-field noncubes #
Mathlib's odd-prime-power binomial irreducibility theorem gives the modulus family. Cauchy's theorem gives a nontrivial cube root of unity when three divides the unit-group order. Cubing is then noninjective and hence nonsurjective on the finite field.
theorem
Algebraic.Cutwidth.Extractor.Internal.binomialModulus_monic
{F : Type u_1}
[Ring F]
(a : F)
(s : ℕ)
:
(binomialModulus a s).Monic
theorem
Algebraic.Cutwidth.Extractor.Internal.binomialModulus_natDegree
{F : Type u_1}
[Ring F]
[Nontrivial F]
(a : F)
(s : ℕ)
:
theorem
Algebraic.Cutwidth.Extractor.Internal.binomialModulus_irreducible
{F : Type u_1}
[Field F]
(a : F)
(s : ℕ)
(noncube : ∀ (b : F), b ^ 3 ≠ a)
:
Irreducible (binomialModulus a s)
theorem
Algebraic.Cutwidth.Extractor.Internal.exists_noncube
{F : Type u_1}
[Field F]
[Fintype F]
(divisible : 3 ∣ Fintype.card F - 1)
:
theorem
Algebraic.Cutwidth.Extractor.Internal.three_dvd_card_sub_one_of_even_exponent
{F : Type u_1}
[Fintype F]
{b : ℕ}
(cardinality : Fintype.card F = 2 ^ b)
(even : Even b)
:
theorem
Algebraic.Cutwidth.Extractor.Internal.binomialModulus_natDegree_clog_bounds
{F : Type u_1}
[Ring F]
[Nontrivial F]
(a : F)
{n : ℕ}
(positive : 0 < n)
:
n ≤ (binomialModulus a (Nat.clog 3 n)).natDegree ∧ (binomialModulus a (Nat.clog 3 n)).natDegree < 3 * n