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Complexitylib.Algebraic.LowerBound.Cutwidth.Extractor.Condenser.Modulus.Binomial.Internal

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_irreducible {F : Type u_1} [Field F] (a : F) (s : ℕ) (noncube : ∀ (b : F), b ^ 3 ≠ a) :
theorem Algebraic.Cutwidth.Extractor.Internal.exists_noncube {F : Type u_1} [Field F] [Fintype F] (divisible : 3 ∣ Fintype.card F - 1) :
∃ (a : F), ∀ (b : F), b ^ 3 ≠ a