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Soundness of the complete nonadaptive long-code test

Lax253009.CNASoundness · concepts/Lax253009/CNASoundness.lean · lax-253009

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    Natural Language Statement

    Theorem

    For every ε>0\varepsilon>0 and positive integer kk, and all sufficiently large ss and then ww, each purported long code AA has a set SS of at most 2εs2^{\varepsilon s} words such that the CNA test, except with probability 2−ks2^{-ks}, either rejects or agrees with evaluation at a word in SS. This is Theorem 4.2 of Håstad's paper.

    The stronger Theorem 4.17 uses the same quantifiers and a set SS chosen independently of the side condition hh. For every hh, except with the same probability, the extended test rejects or agrees with evaluation at some x∈Sx\in S satisfying h(x)h(x).

    The probability is uniform over the ss independently chosen Boolean functions. The thresholds for ss depend only on ε,k\varepsilon,k; the threshold for ww may additionally depend on ss. Both statements concern arbitrary tables, without assuming they are genuine long codes.

    Concept map
    3 concepts; 8 descendants hidden
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    Proven claimDefinitionThis conceptRelated conceptA → B: B builds on A
    Evidence

    This concept declares 2 statements. Each proof establishes one of them relative to its assumptions.

    Lean source view on GitHub

    1import Lax253009.LongCode
    2import Lax253009.FiniteProbability
    3import Mathlib.Analysis.SpecialFunctions.Pow.Real
    4import Mathlib.Data.Fintype.Pi
    5
    6/-!
    7---
    8title: Soundness of the complete nonadaptive long-code test
    9type: theorem
    10---
    11For every ε>0\varepsilon>0 and positive integer kk, and all sufficiently
    12large ss and then ww, each purported long code AA has a set SS of at
    13most 2εs2^{\varepsilon s} words such that the CNA test, except with
    14probability 2−ks2^{-ks}, either rejects or agrees with evaluation at a word
    15in SS. This is Theorem 4.2 of Håstad's paper.
    16
    17The stronger Theorem 4.17 uses the same quantifiers and a set SS chosen
    18independently of the side condition hh. For every hh, except with the
    19same probability, the extended test rejects or agrees with evaluation at
    20some x∈Sx\in S satisfying h(x)h(x).
    21
    22The probability is uniform over the ss independently chosen Boolean
    23functions. The thresholds for ss depend only on ε,k\varepsilon,k; the
    24threshold for ww may additionally depend on ss. Both statements concern
    25arbitrary tables, without assuming they are genuine long codes.
    26-/
    27
    28namespace Lax253009.CNASoundness
    29
    30open LongCode FiniteProbability
    31
    32def Bad {w s : ℕ} (A : Table w) (S : Finset (Word w))
    33 (f : Fin s → Coordinate w) : Prop :=
    34 Accepts A f ∧ ¬ ∃ x ∈ S, LooksLike A f x
    35
    36def BadWithCondition {w s : ℕ} (A : Table w) (S : Finset (Word w))
    37 (h : Coordinate w) (f : Fin s → Coordinate w) : Prop :=
    38 AcceptsWithCondition A f h ∧ ¬ ∃ x ∈ S, h x = true ∧ LooksLike A f x
    39
    40axiom with_side_conditions (ε : ℝ) (hε : 0 < ε) (k : ℕ) (hk : 0 < k) :
    41 ∃ s₀ : ℕ, ∀ s : ℕ, s₀ ≤ s → ∃ w₀ : ℕ, ∀ w : ℕ, w₀ ≤ w →
    42 ∀ A : Table w, ∃ S : Finset (Word w),
    43 (S.card : ℝ) ≤ Real.rpow 2 (ε * (s : ℝ)) ∧
    44 ∀ h : Coordinate w,
    45 probability (BadWithCondition (s := s) A S h) ≤ Real.rpow 2 (-(k : ℝ) * (s : ℝ))
    46
    47axiom without_side_conditions (ε : ℝ) (hε : 0 < ε) (k : ℕ) (hk : 0 < k) :
    48 ∃ s₀ : ℕ, ∀ s : ℕ, s₀ ≤ s → ∃ w₀ : ℕ, ∀ w : ℕ, w₀ ≤ w →
    49 ∀ A : Table w, ∃ S : Finset (Word w),
    50 (S.card : ℝ) ≤ Real.rpow 2 (ε * (s : ℝ)) ∧
    51 probability (Bad (s := s) A S) ≤ Real.rpow 2 (-(k : ℝ) * (s : ℝ))
    52
    53end Lax253009.CNASoundness
    54
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