TECHNICAL R EPORT INSTITUT FUR¨ INFORMATIONSSYSTEME ABTEILUNG DATENBANKEN UND ARTIFICIAL INTELLIGENCE Graph Ramsey games DBAI-TR-99-34 Wolfgang Slany arXiv:cs/9911004v1 [cs.CC] 10 Nov 1999 DBAI TECHNICAL REPORT Institut f¨ur Informationssysteme NOVEMBER 5, 1999 Abteilung Datenbanken und Artificial Intelligence Technische Universit¨at Wien Favoritenstr. 9 A-1040 Vienna, Austria Tel: +43-1-58801-18403 Fax: +43-1-58801-18492
[email protected] http://www.dbai.tuwien.ac.at/ DBAI TECHNICAL REPORT DBAI-TR-99-34, NOVEMBER 5, 1999 Graph Ramsey games Wolfgang Slany1 Abstract. We consider combinatorial avoidance and achievement games based on graph Ramsey theory: The players take turns in coloring still uncolored edges of a graph G, each player being assigned a distinct color, choosing one edge per move. In avoidance games, completing a monochromatic subgraph isomorphic to another graph A leads to immedi- ate defeat or is forbidden and the first player that cannot move loses. In the avoidance+ variants, both players are free to choose more than one edge per move. In achievement games, the first player that completes a monochromatic subgraph isomorphic to A wins. Erd˝os & Selfridge [16] were the first to identify some tractable subcases of these games, followed by a large number of further studies. We complete these investigations by settling the complexity of all unrestricted cases: We prove that general graph Ramsey avoidance, avoidance+, and achievement games and several variants thereof are PSPACE-complete. We ultra-strongly solve some nontrivial instances of graph Ramsey avoidance games that are based on symmetric binary Ramsey numbers and provide strong evidence that all other cases based on symmetric binary Ramsey numbers are effectively intractable.