Cohomological rigidity and the number of homeomorphism types for small covers over prisms

Abstract

In this paper, based upon the basic theory for glued manifolds in M.W. Hirsch (1976) \cite[Chapter 8, \S 2 Gluing Manifolds Together]{h}, we give a method of constructing homeomorphisms between two small covers over simple convex polytopes. As a result we classify, up to homeomorphism, all small covers over a 3-dimensional prism $P^3(m)$ with $m\geq 3$. We introduce two invariants from colored prisms and other two invariants from ordinary cohomology rings with ${\Bbb Z}_2$-coefficients of small covers. These invariants can form a complete invariant system of homeomorphism types of all small covers over a prism in most cases. Then we show that the cohomological rigidity holds for all small covers over a prism $P^3(m)$ (i.e., cohomology rings with ${\Bbb Z}_2$-coefficients of all small covers over a $P^3(m)$ determine their homeomorphism types). In addition, we also calculate the number of homeomorphism types of all small covers over $P^3(m)$.