Conj Aut Xpow eq neg
ArkLib.Lattices.CyclotomicModulus.conjAut_Xpow_eq_neg
Plain-language statement
σ_{-1}(X^e) = -X^{d-e} for 0 < e < d: the conjugate of a sub-d/2 monomial is minus the complementary monomial. The only nonzero coefficient of σ_{-1}(X^e) sits at d - e, with sign -1: from e·conjExp ≡ 2^{α+1} - e (mod 2^{α+1}) we get σ_{-1}(X^e) = X^{d + (d-e)} = -X^{d-e}.
Exact Lean statement
theorem conjAut_Xpow_eq_neg (α : ℕ) {e : ℕ} (he0 : 0 < e) (heα : e < 2 ^ α) :
conjAut α (Xpow (powTwoCyclotomic (R := R) α) e)
= - Xpow (powTwoCyclotomic (R := R) α) (2 ^ α - e)Formal artifact
Lean source
theorem conjAut_Xpow_eq_neg (α : ℕ) {e : ℕ} (he0 : 0 < e) (heα : e < 2 ^ α) : conjAut α (Xpow (powTwoCyclotomic (R := R) α) e) = - Xpow (powTwoCyclotomic (R := R) α) (2 ^ α - e) := by have hc : conjExp α + 1 = 2 ^ (α + 1) := Nat.sub_add_cancel Nat.one_le_two_pow have h2 : (2 : ℕ) ^ (α + 1) = 2 * 2 ^ α := by rw [pow_succ]; ring rw [conjAut_Xpow] have hper : (e * conjExp α) % 2 ^ (α + 1) = (2 ^ α + (2 ^ α - e)) % 2 ^ (α + 1) := by have harith : 2 ^ α + (2 ^ α - e) = 2 ^ (α + 1) - e := by omega rw [harith] have hmod : e * conjExp α ≡ 2 ^ (α + 1) - e [MOD 2 ^ (α + 1)] := by apply Nat.ModEq.add_right_cancel' e rw [Nat.sub_add_cancel (by omega : e ≤ 2 ^ (α + 1))] have hsum : e * conjExp α + e = e * 2 ^ (α + 1) := by rw [← hc]; ring rw [hsum] exact (Nat.modEq_zero_iff_dvd.mpr ⟨e, by ring⟩).trans (Nat.modEq_zero_iff_dvd.mpr (dvd_refl _)).symm exact hmod rw [Xpow_congr_mod α hper, Xpow_add, Xpow_natDegree, neg_one_mul]- Project
- ArkLib
- License
- Apache-2.0
- Commit
- fad5cbf80877
- Source
- ArkLib/Data/Lattices/CyclotomicRing/Subfield/Basis.lean:316-333
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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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Person-level attribution pending.
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Source project: ArkLib
Person-level attribution pending.
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Plain-language statement
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Source project: ArkLib
Person-level attribution pending.