2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/118986In this paper we describe the implementation of the QED process $γγ\toγγ$ through a fermion loop into the framework of SANC system. The computations of this process takes into account non-zero mass of loop-fermion. We briefly describe additional precomputation modules used for calculation of massive fermion-box diagrams. We present the covariant and helicity amplitudes for this process and also some particular cases of $D_0$ and $C_0$ Passarino-Veltman functions. Whenever possible, we compare the results with those existing in the literature.11 pages, 1 figure, Talk presented at the International School-Seminar CALC2006, Dubna, 15-25 July 2006High Energy Physics - Phenomenologytext