  We present the master integrals needed for the light fermionic two-loop
corrections to top quark pair production in the gluon fusion channel. Via the
method of differential equations we compute the results in terms of multiple
polylogarithms in a Laurent series about d=4, where d is the space-time
dimension. The most involved topology is a non-planar double box with one
internal mass. We employ the coproduct-augmented symbol calculus and show that
significant simplifications are possible for selected results using an
optimised set of multiple polylogarithms.
