Mk reverse eq galois Autₛ mul
ArkLib.Lattices.CyclotomicModulus.mk_reverse_eq_galoisAutₛ_mul
Plain-language statement
The reverse identity. In S = Z_q[X]/(X^{2^α}+1), the conjugation σ_{-1} (here the semantic automorphism galoisAutₛ of exponent conjExp = 2^{α+1}-1) and the polynomial reversal are related by mk(reverse p) = σ_{-1}(mk p) · (mk X)^{deg p}. This is the concrete handle behind "σ_{-1} swaps the two factors": since (mk X)^{deg p} is a unit, `σ...
Exact Lean statement
theorem mk_reverse_eq_galoisAutₛ_mul (α : ℕ) (p : (ZMod q)[X]) :
Ideal.Quotient.mk (powTwoCyclotomic (R := ZMod q) α).modIdeal p.reverse
= galoisAutₛ α (conjExp α) (conjExp_odd α)
(Ideal.Quotient.mk (powTwoCyclotomic (R := ZMod q) α).modIdeal p)
* (Ideal.Quotient.mk (powTwoCyclotomic (R := ZMod q) α).modIdeal X) ^ p.natDegreeFormal artifact
Lean source
theorem mk_reverse_eq_galoisAutₛ_mul (α : ℕ) (p : (ZMod q)[X]) : Ideal.Quotient.mk (powTwoCyclotomic (R := ZMod q) α).modIdeal p.reverse = galoisAutₛ α (conjExp α) (conjExp_odd α) (Ideal.Quotient.mk (powTwoCyclotomic (R := ZMod q) α).modIdeal p) * (Ideal.Quotient.mk (powTwoCyclotomic (R := ZMod q) α).modIdeal X) ^ p.natDegree := by set mk := Ideal.Quotient.mk (powTwoCyclotomic (R := ZMod q) α).modIdeal with hmkdef set x : (powTwoCyclotomic (R := ZMod q) α).CyclotomicRing := mk X with hxdef have hx2d : x ^ (2 ^ (α + 1)) = 1 := by rw [hxdef, ← map_pow]; exact mk_X_pow_conductor_eq_one α have hcx : x ^ (conjExp α) * x = 1 := by rw [← pow_succ, conjExp, Nat.sub_add_cancel Nat.one_le_two_pow, hx2d] letI invx : Invertible x := ⟨x ^ (conjExp α), hcx, by rw [mul_comm]; exact hcx⟩ set i : ZMod q →+* (powTwoCyclotomic (R := ZMod q) α).CyclotomicRing := mk.comp C with hidef have heval_mk : ∀ r : (ZMod q)[X], eval₂ i x r = mk r := by have hext : (Polynomial.eval₂RingHom i x) = mk := by apply Polynomial.ringHom_ext · intro a simp only [Polynomial.coe_eval₂RingHom, eval₂_C, hidef, RingHom.comp_apply] · simp only [Polynomial.coe_eval₂RingHom, eval₂_X, hxdef] intro r; rw [← hext]; rfl have hxc : mk (X ^ (conjExp α)) = ⅟x := by rw [map_pow]; rfl have hsigma : galoisAutₛ α (conjExp α) (conjExp_odd α) (mk p) = eval₂ i (⅟x) p := by rw [galoisAutₛ_mk, Polynomial.aeval_def, Polynomial.algebraMap_eq, Polynomial.hom_eval₂, ← hidef, hxc] have hrev := Polynomial.eval₂_reverse_mul_pow i (⅟x) p rw [invOf_invOf, heval_mk, ← hsigma] at hrev rw [← hrev, mul_assoc, ← mul_pow, invOf_mul_self, one_pow, mul_one]- Project
- ArkLib
- License
- Apache-2.0
- Commit
- fad5cbf80877
- Source
- ArkLib/Data/Lattices/CyclotomicRing/Subfield/Field.lean:63-88
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Project documentation
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...
Source project: ArkLib
Person-level attribution pending.
Gadget Decompose coeff
ArkLib.Lattices.Ajtai.gadgetDecompose_coeff
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.
Source project: ArkLib
Person-level attribution pending.
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ArkLib.Lattices.Ajtai.gadgetDecompose_lawful
Plain-language statement
The base-b gadget decomposition is a lawful gadget decomposition.
Source project: ArkLib
Person-level attribution pending.