KKM theorems and discrete geometry beyond matroids

Abstract

We introduce selection structures, a topological framework that extends the role played by color classes and matroids in discrete geometry and KKM theorems. Selection structures allow us to extend classic results to genuinely non-matroidal examples, including chessboard complexes and matching complexes. We show that several matroidal versions of classic results can be generalized to selection structures. These include McGinnis' version of Komiya's KKMS theorem, Holmsen's version of Carathéodory's theorem, Kalai and Meshulam's version of Helly's theorem, and Sadovek's version of the Goodman--Pollack transversal theorem.