  We report on progress for the analytical calculation of the two-loop
corrections to top quark pair production at hadron colliders. For the light
fermionic corrections in the gluon channel, we discuss the analytical solution
for the master integrals of a non-planar double box with a massive propagator.
The result in terms of Goncharov's multiple polylogarithms is handled using
systematic reductions based on the symbol map and the coproduct. We discuss new
features of the computer program Reduze 2. It provides a fully distributed
variant of Laporta's algorithm to reduce loop integrals. New graph matroid
based algorithms allow to calculate shift relations between Feynman integrals
in a fully automated way.
