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Project-declaredLean 4.31.0 · mathlib@fabf563a7c95

Generalised round consistency completeness

RoundConsistency.generalised_round_consistency_completeness

Plain-language statement

Completeness of the round consistency check. Given a polynomial f, challenge γ, and n-th roots of unity ω, when f is honestly evaluated at the scaled points {ω i * s₀}, the round consistency check succeeds with the value (foldNth n f γ).eval (s₀^n). This establishes that the Lagrange interpolant through the evaluation points matches the n-wa...

Exact Lean statement

lemma generalised_round_consistency_completeness
  {𝔽 : Type} [inst1 : Field 𝔽] [DecidableEq 𝔽] {f : Polynomial 𝔽}
  {n : ℕ} [inst : NeZero n]
  {γ : 𝔽}
  {s₀ : 𝔽}
  {ω : Fin n ↪ 𝔽}
  (h : ∀ i, (ω i) ^ n = 1)
  (h₁ : s₀ ≠ 0)
  :
    roundConsistencyCheck
      γ
      (fun i => (ω i * s₀, f.eval (ω i * s₀)))
      ((FoldingPolynomial.polyFold f n γ).eval (s₀ ^ n)) = true

Formal artifact

Lean source

Canonical source
Full Lean sourceLean 4
lemma generalised_round_consistency_completeness  {𝔽 : Type} [inst1 : Field 𝔽] [DecidableEq 𝔽] {f : Polynomial 𝔽}  {n : } [inst : NeZero n]  {γ : 𝔽}  {s₀ : 𝔽}  {ω : Fin n ↪ 𝔽}  (h :  i, (ω i) ^ n = 1)  (h₁ : s₀  0)  :    roundConsistencyCheck      γ      (fun i => (ω i * s₀, f.eval (ω i * s₀)))      ((FoldingPolynomial.polyFold f n γ).eval (s₀ ^ n)) = true := by  unfold roundConsistencyCheck  simp only [beq_iff_eq]  rw [CompPoly.CPolynomial.eval_toPoly,      CompPoly.CPolynomial.CLagrange.cinterpolate_eq_interpolate]  have eval_eval₂_pow_eq_eval_pow {s : 𝔽} (i) :      eval s (eval₂ C (X ^ n) (splitNth f n i)) = (splitNth f n i).eval (s ^ n) := by    rw [eval₂_eq_sum]    unfold Polynomial.eval    rw [Polynomial.eval₂_sum, eval₂_eq_sum]    congr    ext e a    rw [eval]    simp  simp only [polyFold_eq_sum_of_splitNth, map_pow]  rw [eval_finset_sum]  conv =>    rhs    rhs    ext i    rw [eval_mul]    simp   apply Eq.trans (b := eval γ <| ∑ i : Fin n, X ^ (↑i : ) * C (eval (s₀ ^ n) (f.splitNth n i)))  · rw [Lagrange.eq_interpolate:= Fin n)        (v := fun i => ω i * s₀)        (s := Finset.univ)        (f := (∑ i : Fin n, X ^ (↑i : ) * C (eval (s₀ ^ n) (f.splitNth n i)))) (by {    simp only [Finset.coe_univ, Set.injOn_univ]    intro x y hxy    simp at hxy    tauto  }) (by {      simp only [X_pow_mul_C, Finset.card_univ, Fintype.card_fin]      apply lt_of_le_of_lt      · apply Polynomial.degree_sum_le      · simp only [WithBot.bot_lt_natCast, Finset.sup_lt_iff]        intro b _        simp only [degree_mul, degree_pow, degree_X, nsmul_eq_mul, mul_one]        by_cases heq: eval (s₀ ^ n) (f.splitNth n b) = 0        · rw [heq,]          simp        · rw [degree_C]          · simp only [zero_add, Nat.cast_lt, Fin.is_lt]          · tauto    })]    congr    ext i    conv =>      lhs      rw [splitNth_def n f]    rw [eval_finset_sum, eval_finset_sum]    conv =>      lhs      rhs      ext j      rw [eval_mul, eval_eval₂_pow_eq_eval_pow]      simp    conv =>      rhs      rhs      ext j      rw [eval_mul]      simp      rw [one_mul (s₀ ^ n), h i]    rw [mul_pow]  · rw [eval_finset_sum]    conv =>      lhs      rhs      ext i      rw [eval_mul]      simp
Project
ArkLib
License
Apache-2.0
Commit
fad5cbf80877
Source
ArkLib/ProofSystem/Fri/RoundConsistency.lean:42-126

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