Monte Carlo simulations for the ANTARES underwater neutrino telescope. Issue 1 (1st January 2021) - Albert, A.; André, M.; Anghinolfi, M.; Anton, G.; Ardid, M.; Aubert, J.-J.; Aublin, J.; Baret, B.; Basa, S.; Belhorma, B.; Bertin, V.; Biagi, S.; et al.