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The all-edges Exact Triangle host at the middle dimension, assembled as a solver from a Lop-AE-SparseTri solver

Proved
Light.Sec3.mid_solves

by xuanji · Oct 6, 2026 · Mathlib 0df444a (Lean v4.33.1)

apsp-299791apsp-exponentexact-triangleprogram-verification

Let P0P_0P0​ be a program of the light language in which procedure pSp_SpS​ solves Lop-AE-SparseTri (Definition 13 of Alman and Vassilevska Williams, the detection version) within the time Tn(n,D,w)T_n(n,D,w)Tn​(n,D,w) under the need ν\nuν, and in which the procedures pDp_DpD​ and pGp_GpG​ compute the parameter functions D(n)D(n)D(n) and G(D)G(D)G(D): called on x≥1x\ge1x≥1, pDp_DpD​ returns D(x)D(x)D(x) within tD(x)t_D(x)tD​(x) steps, changes no cell and forms only numbers up to wD(x)w_D(x)wD​(x), and likewise pGp_GpG​ with G,tG,wGG,t_G,w_GG,tG​,wG​, in every extension of P0P_0P0​. Assume D(n)≥1D(n)\ge1D(n)≥1 for n≥1n\ge1n≥1.

Append to P0P_0P0​ the 343434 procedures of the all-edges host at the middle dimension, midProcs(pS,pD,pG,∣P0∣)\mathtt{midProcs}(p_S,p_D,p_G,|P_0|)midProcs(pS​,pD​,pG​,∣P0​∣). Then procedure number ∣P0∣+33|P_0|+33∣P0​∣+33 of the resulting program solves All-Edges Exact Triangle within the time

t(n,U)=tfill(n2)+tcore(n,U)+40t(n,U)=t_{\mathrm{fill}}(n^2)+t_{\mathrm{core}}(n,U)+40t(n,U)=tfill​(n2)+tcore​(n,U)+40

under the need νmid(n,U)\nu_{\mathrm{mid}}(n,U)νmid​(n,U), and so does it in every extension of the program. Here All-Edges Exact Triangle on nnn vertices per part with weight bound UUU asks, given wAB,wBC,wAC∈Zn×nw_{AB},w_{BC},w_{AC}\in\mathbb Z^{n\times n}wAB​,wBC​,wAC​∈Zn×n stored in memory, to write to the n2n^2n2 output cells the flag of every pair (a,b)(a,b)(a,b), which is 111 exactly if some ccc has wAB(a,b)+wBC(b,c)+wAC(a,c)=0w_{AB}(a,b)+w_{BC}(b,c)+w_{AC}(a,c)=0wAB​(a,b)+wBC​(b,c)+wAC​(a,c)=0, changing no other cell below the free pointer.

The core time tcore(n,U)t_{\mathrm{core}}(n,U)tcore​(n,U) is the time of computing D=D(n)D=D(n)D=D(n), g=G(D)g=G(D)g=G(D) and the tests, plus either the brute force (if D<16D<16D<16, n<Dn<Dn<D, g<1g<1g<1 or g>⌊D⌋g>\lfloor\sqrt D\rfloorg>⌊D​⌋) or the reduction of Theorem 17: the choice of the prime, the residues, classes and chunks, and at most 4ng4ng4ng calls of the solver at the middle dimension Dm=⌈s/g⌉⋅sD_{\mathrm m}=\lceil s/g\rceil\cdot sDm​=⌈s/g⌉⋅s (s=⌊D⌋s=\lfloor\sqrt D\rfloors=⌊D​⌋) with at most ⌊n2/D⌋\lfloor n^2/\sqrt D\rfloor⌊n2/D​⌋ query pairs each, plus the scans. The need νmid\nu_{\mathrm{mid}}νmid​ adds to the need of the host of Theorem 17 the need of the solver at the middle dimension, and room for the n2n^2n2 flags.

"Procedure ppp solves the task within TTT under the need ν\nuν" means: for every extension of the program, all limits, every depth and every instance in memory satisfying the task's precondition, if the limits meet ν(size,bound)\nu(\text{size},\text{bound})ν(size,bound), the body of ppp ends within T(size,bound)T(\text{size},\text{bound})T(size,bound) steps in a state satisfying the task's postcondition.

Formalization Note The statement is Solves aeTask (P₀ ++ midProcs pS pD pG P₀.length) (P₀.length + 33) (midHostTime Dfun Gfun tD tG Tn) (midHostNeed Dfun Gfun wD wG need) under SolvesN lopDetectTask P₀ pS Tn need, ∀ R, ParamProc (P₀ ++ R) pD Dfun tD wD, ∀ R, ParamProc (P₀ ++ R) pG Gfun tG wG and ∀ n, 1 ≤ n → 1 ≤ Dfun n.

Preamble
/-
Copyright (c) 2026 Anthropic, PBC. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
SPDX-License-Identifier: Apache-2.0
-/
-- Generated by skeleton subtraction from the ThreeSumApsp library at commit 27a2fa4bab32.

import Definitions.Def_APSP299791_Defs5

set_option autoImplicit false
set_option relaxedAutoImplicit false

open Light
open Light.Sec3
open ThreeSumApsp ThreeSumApsp.Spec
variable {P₀ R : Program} {ν : Et17Nums} {pAEBrute pAELoop pScanPairsAE pCore pFill : ℕ}
  {Tn : List ℕ → ℕ} {need : List ℕ → Need} {Dfun Gfun tD tG wD wG : ℕ → ℕ}
Formal statement
theorem Light.Sec3.mid_solves {P₀ : Program} {pS pD pG : ℕ} {Tn : List ℕ → ℕ} {need : List ℕ → Light.Need}
    {Dfun Gfun tD tG wD wG : ℕ → ℕ} (hsol : SolvesN lopDetectTask P₀ pS Tn need)
    (hD : ∀ R, ParamProc (P₀ ++ R) pD Dfun tD wD) (hG : ∀ R, ParamProc (P₀ ++ R) pG Gfun tG wG)
    (hpos : ∀ n, 1 ≤ n → 1 ≤ Dfun n) :
    Solves aeTask (P₀ ++ midProcs pS pD pG P₀.length) (P₀.length + 33)
      (midHostTime Dfun Gfun tD tG Tn) (midHostNeed Dfun Gfun wD wG need) := by sorry
Source
Developed for the prove2.me APSP exponent campaign (https://prove2.me/campaigns/apsp-exponent) on top of the Lean formalization anthropics/formal-math, folder 3sum-apsp, commit e1a4e65 (https://github.com/anthropics/formal-math/tree/e1a4e6508154ea59f030480661590a9fe3018011/3sum-apsp; Lean v4.33.1, Mathlib v4.33.1). The statement comes from the file 3sum-apsp/ThreeSumApsp/AllEdges/MidHost.lean of the campaign's modified copy of that library, which is not published; the new and modified definitions it uses are in the platform definition bundles APSP299791_Defs1 to APSP299791_Defs5. It builds on J. Alman and V. Vassilevska Williams, "Truly Subquadratic 3SUM and Truly Subcubic APSP via Triangles in Sparse Lopsided Graphs", arXiv:2610.06783v1 (https://arxiv.org/abs/2610.06783v1), Theorem 17 (p. 33), Definition 13 (p. 31). This result belongs to an improvement of the paper's bounds developed for this campaign and is not stated in the paper.

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