RL unknotter, hard unknots and unknotting number

arXiv stat.ML / 4/7/2026

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Key Points

  • The paper presents a reinforcement learning pipeline that simplifies knot diagrams by learning move proposals and a value heuristic to guide Reidemeister moves.
  • The approach is designed to work on arbitrary knots and links, including challenging unknot diagrams identified as “very hard.”
  • By using diagram inflation, the authors demonstrate the ability to recover a recently established and surprising upper bound of three for the unknotting number of the knot/link form 4_1#9_10.
  • The work also introduces a self-improving, workbook-driven extension that iteratively strengthens upper bounds for the unknotting number across a list of prime knots.

Abstract

We develop a reinforcement learning pipeline for simplifying knot diagrams. A trained agent learns move proposals and a value heuristic for navigating Reidemeister moves. The pipeline applies to arbitrary knots and links; we test it on ``very hard'' unknot diagrams and, using diagram inflation, on 4_1\#9_{10} where we recover the recently established and surprising upper bound of three for the unknotting number. In addition, we explain a self-improving workbook-driven extension of the pipeline that systematically improves unknotting number upper bounds on the list of prime knots.