On the geometric realization and subdivisions of dihedral sets

We extend to dihedral sets Drinfeld's filtered-colimit expressions of the geometric realization of simplicial and cyclic sets. We prove that the group of homeomorphisms of the circle continuously act on the geometric realization of a dihedral set. We also see how these expressions of geometric realization clarify subdivision operations on simplicial, cyclic and dihedral sets defined by Bokstedt, Hsiang and Madsen, and Spalinski.