$Z\gamma\gamma\gamma\to 0$ processes in SANC
  In this paper we describe the analytic and numerical evaluation of the $\gamma\gamma\to \gamma Z$ process cross section and the $Z\to \gamma\gamma\gamma$ decay rate within the SANC system multi-channel approach at the one-loop accuracy level with all masses taking into account. The corresponding package for numeric calculations is presented. For checking of the results correctness we make a comparison with other independent calculations. 
D. Bardin, L. Kalinovskaya, E. Uglov
hep-ph