The directed Generalized Geography game is well-known to be PSPACE-complete, however, I could not find anything for the undirected version. I saw that in Hans L. Bodlaender, Complexity of path-forming games, Theoretical Computer Science, Volume 110, Issue 1, 15 March 1993, Pages 215-245 (thx to Marzio De Biasi for the link) it is posed as an open problem. Is it still open?

In fact, I wonder if there is a simple gadget that we can put in the place of every directed edge to make a straight-forward reduction from the directed version. Is it known that no such gadget can exist?


1 Answer 1


Undirected (Vertex) Geography is in P. In particular, the game on graph $G$ with starting vertex $v$ is a win for player 1 if and only if every maximum matching of $G$ uses the vertex $v$. This can be checked in polynomial time.

The above is Theorem 1.1 from the paper "Undirected Edge Geography", by Fraenkel, Scheinerman and Ullman, Theoretical Computer Science 1993.


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