The unpinning avoidance game PSPACE-completeness conjecture

From papers

Let γ ⁣:i=1sS1Σ\gamma\colon\bigsqcup_{i=1}^s S^1\looparrowright\Sigma be a multiloop on a surface Σ\Sigma. In the unpinning avoidance game, two players alternately remove pins while leaving a pinning set after each turn; the first player with no legal move loses. Let UnpinAVOID(Σ,s)\mathsf{Unpin_{AVOID}}(\Sigma,s) be the decision problem asking whether Player 1 has a winning strategy, and let SimpleUnpinAVOID(Σ,s)\mathsf{SimpleUnpin_{AVOID}}(\Sigma,s) be its restriction to simple multiloops.

Unpinning avoidance game complexity conjecture. The problem UnpinAVOID(Σ,s)\mathsf{Unpin_{AVOID}}(\Sigma,s) is PSPACE\textsf{PSPACE}-complete for any ss and Σ\Sigma, and SimpleUnpinAVOID(Σ,s)\mathsf{SimpleUnpin_{AVOID}}(\Sigma,s) is PSPACE\textsf{PSPACE}-complete for any s4s\geq 4.

The conjecture is motivated by the relationship with Node Kayles, which is known to be PSPACE\textsf{PSPACE}-complete, but the paper leaves these game-complexity claims unresolved.

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Sources & referencesView supporting material

Primary source

Eric Seo, Christopher-Lloyd Simon and Ben Stucky, “The complexity of pinning simple multiloops”, arXiv:2602.07344 (2026).

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