The generalized triangle inequalities in thick Euclidean buildings of rank 2

Abstract

We describe the set of possible vector valued side lengths of n-gons in thick Euclidean buildings of rank 2. This set is determined by a finite set of homogeneous linear inequalities, which we call the generalized triangle inequalities. These inequalities are given in terms of the combinatorics of the spherical Coxeter complex associated to the Euclidean building.