tB_getD (KFY 16: the `A` pass and the `B₀` pass)

Proved

NLogN.KFY.tB_getD

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

complexity-theoryinteger-multiplicationkappa-improvement

The following holds (Lean statement, in the scope of module Solutions.KFY16PassAB):

theorem NLogN.KFY.tB_getD {n k : ℕ} (hn : IntMul.OpenAI.Glue.n0 ≤ n) (hk : k < IntMul.OpenAI.Glue.dP n) :
    (List.ofFn (KFM.tB n)).getD k 1 = tN n k

Context. The lemma belongs to the part KFY 16: the A pass and the B₀ pass: The arrays keep the invariant length = ∏ t_i, DiscL p (which gives GB (p + 2)), using an M : AxisMaps (disc_sapL, disc_b0Pad).

Formalization Note. This lemma belongs to layer 5 of the Lean formalization (integer-multiplication-kappa campaign) of the OpenAI preprint Integer multiplication below $n\log n$ : 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 linter.unusedSectionVars false
open NLogN
open NLogN.KFY
open IntMul NLogN IntMul.HvdH.Ref NLogN.GL NLogN.AX NLogN.Rsp

Formal statement

theorem NLogN.KFY.tB_getD {n k : ℕ} (hn : IntMul.OpenAI.Glue.n0 ≤ n) (hk : k < IntMul.OpenAI.Glue.dP n) :
    (List.ofFn (KFM.tB n)).getD k 1 = tN n k := 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.KFY.tB_getD` of the Lean development Solutions/KFY16PassAB.lean (lines 43–45), integer-multiplication-kappa campaign.

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