The Baum-Connes conjecture (BC) is a far-reaching generalization of the Atiyah-Singer index theorem. It uses index theory to establish a link (assembly map) between the K-theory of convolution algebras of geometric origin (analytical side) with homological invariants of the geometric situation involved (topological side), and conjectures that it is an equivalence. Counterexamples to BC were given by Higson, V. Lafforgue and Skandalis.
