2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/227661We apply the recently proposed amplitude reduction at the integrand level method, to the computation of the scattering process 2 photons -> 4 photons, including the case of a massive fermion loop. We also present several improvements of the method, including a general strategy to reconstruct the rational part of any one-loop amplitude and the treatment of vanishing Gram-determinants.21 pages, 3 figures. Version accepted for publication in JHEPHigh Energy Physics - Phenomenologytext