Leonid Pavlovych Nyzhnyk (on his 70-th birthday) - Berezansky, Yu. M.; Gorbachuk, V. I.; Gorbachuk, M. L.; Kostyuchenko, A. G.; Kuzhel', S. A.; Marchenko, V. O.; Samoilenko, A. M.; Samoilenko, Yu. S.; Khruslov, E. Ya. (Ukrains’kyi Matematychnyi Zhurnal, 2005)