Breakthrough Tracker record

An explicit construction disproves the undirected multiple-unicast conjecture

Braverman and He construct an undirected network with 157 independent sessions whose linear network-coding rate is at least 1 while fractional multicommodity flow is at most 147/157, and use amplification to obtain a polylogarithmic coding gap.

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Stable ID
cs-undirected-multiple-unicast-counterexample-2026
Revision
cs-undirected-multiple-unicast-counterexample-2026.v1
Field
Theoretical computer science · Network coding, information theory and theoretical computer science
Evidence
Tier 1 · Peer reviewed: No
Record state
Provisional · Explicit verifier-backed preprint counterexample
Last checked

AI role

The authors report that GPT-6 found a nondeterministic design. They converted it into a causal construction, applied orientation and local search, and supplied an exact symbolic verifier and simulator.

Record details

Problem or result
Undirected multiple-unicast network-coding conjecture
Authors
Mark Braverman and Zhongtian He
Institutions
Princeton University
Result date
Preprint submitted October 7, 2026

Why it matters

The paper supplies a finite explicit witness against a long-standing network-coding conjecture rather than only an existential separation.

Limits

The executable checker is author-supplied rather than an independent replication, the amplified family depends on the cited theorem, and the large construction has not been peer reviewed or independently replayed in the sources checked.

Sources

  1. Primary: Braverman and He multiple-unicast counterexample
  2. Verification artifact: Counterexample symbolic verifier and simulator

Correction and revision history

  1. 2026-10-19 — Added after primary-source, scope, status, AI-role and limitation review.

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