On the geometric realization and subdivisions of dihedral sets

By expressing the geometric realization of simplicial sets and cyclic sets as filtered colimits, Drinfeld (arXiv:math/0304064v3) proved in a substantially simplified way the fundamental facts that geometric realization preserves finite limits, and that the group of orientation-preserving homeomorphisms of the interval [0,1] (resp. the circle R/Z) acts on the realization of a simplicial (resp. cyclic) set. In this paper, we first review Drinfeld's method and then introduce an analogous expression for the geometric realization of dihedral sets. We also see how these expressions lead to a clarified description of subdivisions of simplicial, cyclic, and dihedral sets.