This book develops the central aspect of fixed point theory - the topological fixed point index - to maximal generality, emphasizing correspondences and other aspects of the theory that are of special interest to economics. Numerous topological consequences are presented, along with important...

We introduce a combinatorial abstraction of two person finite games in an oriented matroid. We also define a combinatorial version of Nash equilibrium and prove that an odd number of equilibria exists. The proof is a purely combinatorial rendition of the Lemke-Howson algorithm