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Project-declaredLean 4.31.0 · mathlib@fabf563a7c95

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

Canonical source
Full Lean sourceLean 4
theorem conjAut_Xpow_eq_neg (α : ) {e : } (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 ^+ 1) := Nat.sub_add_cancel Nat.one_le_two_pow  have h2 : (2 : ) ^+ 1) = 2 * 2 ^ α := by rw [pow_succ]; ring  rw [conjAut_Xpow]  have hper : (e * conjExp α) % 2 ^+ 1) = (2 ^ α + (2 ^ α - e)) % 2 ^+ 1) := by    have harith : 2 ^ α + (2 ^ α - e) = 2 ^+ 1) - e := by omega    rw [harith]    have hmod : e * conjExp α ≡ 2 ^+ 1) - e [MOD 2 ^+ 1)] := by      apply Nat.ModEq.add_right_cancel' e      rw [Nat.sub_add_cancel (by omega : e  2 ^+ 1))]      have hsum : e * conjExp α + e = e * 2 ^+ 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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Plain-language statement

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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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