A composite boson is a bound state of fermions such that the combination gives a boson. Examples include Cooper pairs, semiconductor excitons, mesons, superfluid helium, Bose–Einstein condensates, atomic bosons, and fermionic condensates. A composite particle containing an even number of fermions is a boson, since it has integer spin. These composite particle states have a symmetric wave function upon exchange of any pair of particles. The wave function is given by the permanent of single particle states for the non interacting case.