  Gluon fusion processes like single and double Higgs production exhibit slow
convergence and pose severe computational challenges. We show how the top-quark
mass dependence of the virtual amplitudes can be reconstructed with a conformal
mapping and Pad\'e approximants based on the expansion in the inverse top-quark
mass and the non-analytic terms in the expansion around the top threshold. The
method is then applied at two- and three-loop order.
