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Project-declaredLean 4.31.0 · mathlib@fabf563a7c95

Order Of q mod two pow

ArkLib.Lattices.CyclotomicModulus.orderOf_q_mod_two_pow

Plain-language statement

The multiplicative order of q modulo 2^(α+1) is 2^(α-1), phrased to match ZMod.irreducible_of_dvd_cyclotomic_of_natDegree (K = ZMod q, n = 2^(α+1)).

Exact Lean statement

theorem orderOf_q_mod_two_pow (hq5 : q % 8 = 5) (α : ℕ) (hα : 1 ≤ α) :
    orderOf (ZMod.unitOfCoprime q (coprime_q_two_pow hq5 (α + 1))) = 2 ^ (α - 1)

Formal artifact

Lean source

Canonical source
Full Lean sourceLean 4
theorem orderOf_q_mod_two_pow (hq5 : q % 8 = 5) (α : ) (hα : 1  α) :    orderOf (ZMod.unitOfCoprime q (coprime_q_two_pow hq5 (α + 1))) = 2 ^- 1) := by  rcases Nat.lt_or_ge α 2 with hlt | hge  · have hα1 : α = 1 := by omega    subst hα1    simp only [Nat.sub_self, pow_zero]    rw [orderOf_eq_one_iff,  pow_one (ZMod.unitOfCoprime q _), unit_pow_eq_one_iff hq5 1 1]    simpa using four_dvd_q_sub_one hq5  · have key := orderOf_eq_prime_pow (x := ZMod.unitOfCoprime q (coprime_q_two_pow hq5 (α + 1)))      (p := 2) (n := α - 2) ?_ ?_    · rw [key]; congr 1; omega    · rw [unit_pow_eq_one_iff hq5 α]      have h3 := not_two_pow_dvd (q := q) hq5 (α - 2)      have he : (α - 2) + 3 = α + 1 := by omega      rwa [he] at h3    · rw [unit_pow_eq_one_iff hq5 α]      have h2 := two_pow_dvd (q := q) hq5 (α - 1)      have he : (α - 1) + 2 = α + 1 := by omega      have he2 : (α - 2) + 1 = α - 1 := by omega      rw [he2]; rwa [he] at h2
Project
ArkLib
License
Apache-2.0
Commit
fad5cbf80877
Source
ArkLib/Data/Lattices/CyclotomicRing/NormBounds/LsCore.lean:152-171

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This lemma proves the final algebraic step in the DG25 Theorem 3.1 proof. It shows that if R > e + 1, then e * (R / (R - 1)) < e + 1. The intuition is that the fraction R / (R - 1) is always greater than 1, but as R gets larger, it gets closer to 1. The hypothesis R > e + 1 provides a strong enough bound to ensure the product e * (fraction) do...

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Project-declaredLean 4.31.0

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Plain-language statement

The k-th coefficient (k < deg φ) of a gadget-decomposition block is exactly the corresponding digit of the corresponding input coefficient.

cryptographyproof systemscoding theory

Source project: ArkLib

Person-level attribution pending.

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Project-declaredLean 4.31.0

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ArkLib.Lattices.Ajtai.gadgetDecompose_lawful

Plain-language statement

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cryptographyproof systemscoding theory

Source project: ArkLib

Person-level attribution pending.

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