Involutory Hopf group-coalgebras and flat bundles over 3-manifolds
Involutory Hopf group-coalgebras and flat bundles over 3-manifolds
Given a group $\pi$, we use involutory Hopf $\pi$-coalgebras to define a scalar invariant of flat $\pi$-bundles over 3-manifolds. When $\pi=1$, this invariant equals the one for 3-manifolds constructed by Kuperberg from involutory Hopf algebras. We give