3SUM asks whether three distinct positions in a list of integers contain values summing to zero. It is a central problem in fine-grained complexity.
This mission formalizes a deterministic algorithm for 3SUM on polynomially bounded integers, on a word RAM with -bit words. Alman and Vassilevska Williams's 2026 breakthrough gives a truly subquadratic bound, refuting the integer 3SUM hypothesis in this model.
The mission uses the accompanying Lean specification and shares the Exact Triangle milestone with Truly Subcubic APSP on a Word RAM.
Theorem_22_3SUM.theorem TrulySubquadratic3SUM.threeSum :
EndStatement.ThreeSum.SolvedInTime 1.9992 := by sorryFor every fixed , there exist a finite deterministic word-RAM program , a natural constant , and a step-bound function that work for every input size and every word width . Given integers with , the program halts within steps and accepts if and only if there are pairwise distinct indices such that .
The time bound is : precisely, there is a natural constant such that for every . The program must also halt and reject when . Repeated integer values at different positions are allowed; no witness triple needs to be output.
This is exactly EndStatement.Theorem_22_3SUM from the accompanying formalization. It is the integer 3SUM part of Theorem 22, using Corollary 26, presented here as an open proof obligation.
No open leaves. Every sub-goal is proved or awaiting decomposition.