Bounded differential forms and coinvariants of bounded functions

Given a group $G$ acting cocompactly on a smooth manifold $M$ by deck transformations, there is an integration map, defined recently by Kato, Kishimoto and Tsutaya, from the top-degree bounded de Rham cohomology of $M$ to the coinvariants $\ell^\infty(G)_G$. We generalize its definition and show that it is an isomorphism. In the presence of boundary, a relative version of bounded de Rham cohomology is considered.