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The read-out

Proved
NLogN.KFM.fin_phase

by xuanji · Oct 17, 2026 · Mathlib 0df444a (Lean v4.33.1)

complexity-theoryinteger-multiplicationkappa-improvement

The read-out.

The following holds (Lean statement, in the scope of module Solutions.KFMBig9):

theorem NLogN.KFM.fin_phase (C : BigCtx ix Isym extM n D) (t : IState HS) (hR : BaseOK t n) (x y : ℕ)
    (hx : x < 2 ^ n) (hy : y < 2 ^ n) (zsZ : List GI)
    (Z : ((i : Fin (D + 1)) → ZMod (sBD n D i)) → ℂ)
    (h0 : t.G 0 = ints (gflat zsZ)) (hZ : RepPad (pP n) (sBD n D) (tBD n D) zsZ Z)
    (hg : NLogN.KFB.GB (NLogN.KFM.wU n D) zsZ) (hcl : Close C x y Z) (hout : t.out = []) :
    ∃ s' c, IRuns Isym (kTable extM) (finP ix) t s' c ∧ s'.out = bin (2 * n) (x * y) ∧
      (c : ℝ) ≤ kFin C

Context. The lemma belongs to the part KFM Big9: the read-out: After the rounding passes (finA), Φ⁻¹; carries; write outputs bin(2n, x·y).

Formalization Note. This lemma belongs to layer 5 of the Lean formalization (integer-multiplication-kappa campaign) of the OpenAI preprint Integer multiplication below nlog⁡nn\log nnlogn: the uniform item-language machine (register programs over the NLogN multitape framework) assembling the Proposition 14 / Lemma 13 / Proposition 18 pieces, the resampling and chirp stages and the cost recurrences into one fixed machine, culminating in NLogN.KFTop.kappa_bound : IntMul.KappaBound (1 / 2 ^ 182) (the bound of Def_IntMul_MultitapeModel). All names refer to the definition bundles up to IntMul_Kappa_K_Defs33.

Preamble
-- OpenAI-preprint / κ-improvement development (integer-multiplication-kappa), generated by skeleton subtraction.

import Definitions.Def_IntMul_Kappa_K_Defs33

set_option autoImplicit false
set_option relaxedAutoImplicit false
set_option maxHeartbeats 1000000

set_option linter.unusedSimpArgs false
set_option linter.unusedVariables false
set_option maxRecDepth 20000
open NLogN
open NLogN.KFM
open Finset AModel AModelL12 IntMul KIL KFB KFT KFU RS IntMul.HvdH IntMul.OpenAI.RT
  IntMul.OpenAI.RC IntMul.OpenAI.Glue IntMul.OpenAI.RCost
variable {E : ℕ} {ix : Ix (7 + E)} {Isym : List Sym} {extM : Fin E → IStmt HS (7 + E)} {n D : ℕ}
  [instS : ∀ i, NeZero (sBD n D i)] [instT : ∀ i, NeZero (tBD n D i)]
set_option maxHeartbeats 8000000
Formal statement
theorem NLogN.KFM.fin_phase (C : BigCtx ix Isym extM n D) (t : IState HS) (hR : BaseOK t n) (x y : ℕ)
    (hx : x < 2 ^ n) (hy : y < 2 ^ n) (zsZ : List GI)
    (Z : ((i : Fin (D + 1)) → ZMod (sBD n D i)) → ℂ)
    (h0 : t.G 0 = ints (gflat zsZ)) (hZ : RepPad (pP n) (sBD n D) (tBD n D) zsZ Z)
    (hg : NLogN.KFB.GB (NLogN.KFM.wU n D) zsZ) (hcl : Close C x y Z) (hout : t.out = []) :
    ∃ s' c, IRuns Isym (kTable extM) (finP ix) t s' c ∧ s'.out = bin (2 * n) (x * y) ∧
      (c : ℝ) ≤ kFin C := by sorry
Source
OpenAI, Integer multiplication below n log n (preprint, 23 Sep 2026), https://github.com/openai/math/tree/adc7f1241b42e322a6451854ab7e4b4c146bf78a/preprints/Integer-multiplication-below-n-log-n-September-23-2026. Lemma `NLogN.KFM.fin_phase` of the Lean development Solutions/KFMBig9.lean (lines 197–298), integer-multiplication-kappa campaign.

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