  We report on recent progress in calculating the three loop QCD corrections of
the heavy flavor contributions in deep--inelastic scattering and the massive
operator matrix elements of the variable flavor number scheme. Notably we deal
with the operator matrix elements $A_{gg,Q}^{(3)}$ and $A_{Qg}^{(3)}$ and
technical steps to their calculation. In particular, a new method to obtain the
inverse Mellin transform without computing the corresponding $N$--space
expressions is discussed.
