On the 60th birthday of Leonid Pavlovich Nizhnik - Berezansky, Yu. M.; Gorbachuk, V. I.; Gorbachuk, M. L.; Korolyuk, V. S.; Mitropolskiy, Yu. A.; Samoilenko, A. M.; Tarasov, V. G. (Ukrains’kyi Matematychnyi Zhurnal, 1995)