A multitriangulation of order k, or a k-triangulation, of a convex n-gon is a maximal set of diagonals such that no k+1 of them mutually cross in the interior of the n-gon. First studied in the 1992 paper “A Turán-Type Theorem on the Chords of Convex Polygons” by Capoyleas and Pach, k-triangulations have recently been studied in the context of the multi-associahedron. In this talk, we will prove a result by Pilaud and Santos in the paper “Multi-triangulations as Complexes of Star Polygons”, namely, that k-triangulations are formed by a union of k-stars and “k-irrelevant” edges. Time permitting, we will also discuss our recent work concerning the realization of the multi-associahedron.

Injective modules play an important role in various algebraic questions.  We will introduce the notion of an injective module and show that any module can be embedded in an injective module in a minimal way.  This is a result originally given by B. Eckmann and A. Schopf.