Resumen de The fixed point theorem for simplicial nonpositive curvature
We prove that for an action of a finite group G on a systolic complex X there exists a G-invariant subcomplex of X of diameter =5. For 7-systolic locally finite complexes we prove there is a fixed point for the action of any finite G. This implies that free products with amalgamation (and HNN extensions) of 7-systolic groups over finite subgroups are also 7-systolic.
