Soundness of the complete nonadaptive long-code test
Lax253009.CNASoundness · concepts/Lax253009/CNASoundness.lean · lax-253009
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Theorem
For every and positive integer , and all sufficiently large and then , each purported long code has a set of at most words such that the CNA test, except with probability , either rejects or agrees with evaluation at a word in . This is Theorem 4.2 of Håstad's paper.
The stronger Theorem 4.17 uses the same quantifiers and a set chosen independently of the side condition . For every , except with the same probability, the extended test rejects or agrees with evaluation at some satisfying .
The probability is uniform over the independently chosen Boolean functions. The thresholds for depend only on ; the threshold for may additionally depend on . Both statements concern arbitrary tables, without assuming they are genuine long codes.
Concept map
Evidence
Lean source view on GitHub
| 1 | import Lax253009.LongCode |
| 2 | import Lax253009.FiniteProbability |
| 3 | import Mathlib.Analysis.SpecialFunctions.Pow.Real |
| 4 | import Mathlib.Data.Fintype.Pi |
| 5 | |
| 6 | /-! |
| 7 | --- |
| 8 | title: Soundness of the complete nonadaptive long-code test |
| 9 | type: theorem |
| 10 | --- |
| 11 | For every and positive integer , and all sufficiently |
| 12 | large and then , each purported long code has a set of at |
| 13 | most words such that the CNA test, except with |
| 14 | probability , either rejects or agrees with evaluation at a word |
| 15 | in . This is Theorem 4.2 of Håstad's paper. |
| 16 | |
| 17 | The stronger Theorem 4.17 uses the same quantifiers and a set chosen |
| 18 | independently of the side condition . For every , except with the |
| 19 | same probability, the extended test rejects or agrees with evaluation at |
| 20 | some satisfying . |
| 21 | |
| 22 | The probability is uniform over the independently chosen Boolean |
| 23 | functions. The thresholds for depend only on ; the |
| 24 | threshold for may additionally depend on . Both statements concern |
| 25 | arbitrary tables, without assuming they are genuine long codes. |
| 26 | -/ |
| 27 | |
| 28 | namespace Lax253009.CNASoundness |
| 29 | |
| 30 | open LongCode FiniteProbability |
| 31 | |
| 32 | def 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 | |
| 36 | def 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 | |
| 40 | axiom 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 | |
| 47 | axiom 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 | |
| 53 | end Lax253009.CNASoundness |
| 54 |
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