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Project-declaredLean 4.31.0 · mathlib@fabf563a7c95

Log right inverse

Domain.CosetFftDomainClass.log_right_inverse'

Plain-language statement

Evaluating ω at the index found by log recovers x.

Exact Lean statement

@[simp]
lemma log_right_inverse' {ω : D} {x : ω} :
  ω (log ω x) = x

Formal artifact

Lean source

Canonical source
Full Lean sourceLean 4
@[simp]lemma log_right_inverse' {ω : D} {x : ω} :  ω (log ω x) = x := by  have h_log :  i : Fin (2 ^ n), ω i = x := by    exact Finset.mem_image.mp x.2 |> fun i, _, hi  i, hi  obtain i, hi := h_log  have h_log_aux :     (fuel : ) (i : Fin (2 ^ n)),      i.val < fuel  ω i = x  ω (logAux ω x fuel) = x := by    intro fuel i hi hx    induction fuel generalizing i with    | zero => simp_all    | succ fuel ih =>      by_cases hfuel : fuel < 2 ^ n      · by_cases hfound : ω (fuel, hfuel : Fin (2 ^ n)) = x        · simp [logAux, hfuel, hfound]        · rw [show logAux ω x (fuel + 1) = logAux ω x fuel by simp [logAux, hfuel, hfound]]          apply ih i          · have hi_ne : i.val  fuel := by              intro hval              apply hfound              have hfin : i = (fuel, hfuel : Fin (2 ^ n)) := Fin.ext hval              rw [ hfin]              exact hx            omega          · exact hx      · rw [show logAux ω x (fuel + 1) = logAux ω x fuel by simp [logAux, hfuel]]        apply ih i        · exact lt_of_lt_of_le i.isLt (Nat.le_of_not_gt hfuel)        · exact hx  exact h_log_aux _ _ (Fin.is_lt i) hi
Project
ArkLib
License
Apache-2.0
Commit
fad5cbf80877
Source
ArkLib/Data/Domain/CosetFftDomain/Log.lean:61-91

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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...

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Project-declaredLean 4.31.0

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.

cryptographyproof systemscoding theory

Source project: ArkLib

Person-level attribution pending.

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Project-declaredLean 4.31.0

Gadget Decompose lawful

ArkLib.Lattices.Ajtai.gadgetDecompose_lawful

Plain-language statement

The base-b gadget decomposition is a lawful gadget decomposition.

cryptographyproof systemscoding theory

Source project: ArkLib

Person-level attribution pending.

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