Light-by-light scattering in SANC

In this paper we describe the implementation of the QED process $\gamma\gamma\to\gamma\gamma$ 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.