Abstract
Abstract: A cellular string of a polytope is a sequence of faces of the polytope that are stacked
on top of each other in a particular direction. The collection of cellular strings, ordered by refinement,
forms a poset that is homotopy equivalent to a sphere. Among the set of strings, the subposet of coherent
ones is homeomorphic to a sphere. In this talk, I will give an oriented matroid characterization of zonotopes
whose poset of cellular strings is a sphere, i.e. for which all strings are coherent. This is based on joint work
with Rob Edman, Pakawut Jiradilok, and Gaku Liu.