  Real and virtual corrections in NNLO QCD require multi-dimensional integrals
with overlapping singularities. We first review ideas and methods which have
been proposed for performing such computations. We then present a new method
for the factorization of overlapping singularities based on non-linear integral
transformations. We apply this method for the evaluation of all integral
topologies which appear in double real radiation corrections in cross-section
calculations for the production of a heavy system at hadron colliders. Finally,
we demonstrate with typical examples that two-loop virtual corrections are
amenable to the same method.
