Searching for Stage Proof Number in Connect6

This study proposes a search architecture called Stage Proof Number Search, and performs a best-first search in an AND/OR game tree. The search surveys numerous candidate moves to prove or disprove a sudden-death property, and Threat Space Search (TSS) is the sudden-death for Connect6. Generating Threat-Move is the core part of TSS. This study proposes an elegant algorithm for Threat-Move generation. The experimental results show that the new search architecture is significantly more efficient than standard PNS on positions for which TSS solutions are available in Connect6.