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`ℓ ≥ C (log₂ b + 1)^2` for large `n` (round six, `ell_big`)

Proved
IntMul.Kappa.R6.ell_big

by xuanji · Oct 20, 2026 · Mathlib 0df444a (Lean v4.33.1)

complexity-theoryinteger-multiplicationkappa-improvement

ℓ ≥ C (log₂ b + 1)^2 for large n.

The following holds (Lean statement, in the scope of module Solutions.R6SMath):

theorem IntMul.Kappa.R6.ell_big (P : Prm) (hP : P.Ok) (C : ℕ) :
    ∃ n₁ : ℕ, ∀ n, n₁ ≤ n → C * (Nat.log 2 (bP6 n) + 1) ^ 2 ≤ ℓP6 P n

Context. Round-six setup, part 1: the sources by search, and the counted parameters

The setup machine picks the source s_j of axis j by scanning the candidates c = A_j + x (A_j = t_j - 2 w_j, x = w_j, w_j - 1, …, 1) and keeping the last one coprime to 2 ∏_{i<j} s_i (pick, src6). The sieve (J6SieveStep.step) shows that a coprime candidate exists once w_j > sieveBound d r (exists_cop), which holds for large n (ell_big: ℓ ≥ C (log₂ b + 1)^2 eventually). Then src6 satisfies SrcOK6 (src6_ok).

The parameters d, L, α are computed by the machine as counts (d_count6, L_count6, α_count6).

Formalization Note. Part of the Lean formalization of the round-six κ-improvement (integer-multiplication-kappa campaign, target IntMul.Kappa.jain_round6_framework). The statement is copied verbatim from the Lean development; the platform node carries the same declaration name. Definitions it mentions live in the IntMul_Kappa_R6_Defs* bundles (on top of the published κ bundles IntMul_Kappa_K_Defs*).

Preamble
-- Round-six κ development (integer-multiplication-kappa), generated by skeleton subtraction.

import Definitions.Def_IntMul_Kappa_K_Defs33
import Definitions.Def_IntMul_Kappa_R6_Defs1
import Mathlib
import Definitions.Def_IntMul_HvdH_M_Defs8
import Definitions.Def_IntMul_MultitapeModel
import Definitions.Def_IntMul_HvdH_Numeric
import Definitions.Def_IntMul_HvdH_ExpApprox
import Definitions.Def_IntMul_HvdH_Twiddle
import Definitions.Def_IntMul_HvdH_RealExp
import Definitions.Def_IntMul_HvdH_MachineRef
import Definitions.Def_IntMul_HvdH_SApprox
import Definitions.Def_IntMul_HvdH_DiagApprox
import Definitions.Def_IntMul_HvdH_EApprox
import Definitions.Def_IntMul_HvdH_JApprox
import Definitions.Def_IntMul_HvdH_BApprox
import Definitions.Def_IntMul_HvdH_FPApprox
import Definitions.Def_IntMul_KappaFramework
import Definitions.Def_IntMul_KappaJainData

set_option autoImplicit false
set_option relaxedAutoImplicit false
set_option maxHeartbeats 1000000

open IntMul IntMul.Kappa IntMul.Kappa.R6
open IntMul NLogN NLogN.KFM Finset
Formal statement
theorem IntMul.Kappa.R6.ell_big (P : Prm) (hP : P.Ok) (C : ℕ) :
    ∃ n₁ : ℕ, ∀ n, n₁ ≤ n → C * (Nat.log 2 (bP6 n) + 1) ^ 2 ≤ ℓP6 P n := by sorry
Source
S. Jain, round-six networks for the integer-multiplication κ-improvement campaign (https://github.com/Swapnil-jain/integer-mult-kappa, commit 5868dc7) and D. Colkitt, integer-mult-bounds (https://github.com/CrocSwap/integer-mult-bounds); target `IntMul.Kappa.jain_round6_framework`. Lean declaration `IntMul.Kappa.R6.ell_big`, Solutions/R6SMath.lean (lines 185–247) of the round-six development.

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