Advances in Optimization and Applications 12th International Conference, OPTIMA 2021, Petrovac, Montenegro, September 27 – October 1, 2021, Revised Selected Papers - Olenev, Nicholas N.; Evtushenko, Yuri G.; Jaćimović, Milojica; Khachay, Michael; Malkova, Vlasta (Communications in Computer and Information Science, 2021)