Mykola Ivanovych Portenko (on his 80th birthday)

Authors

• B. I. Kopytko Czestochowa University of Technology https://orcid.org/0000-0003-3793-4838
• M. M. Osypchuk Prykarpattia National University named after Vasyl Stefanyk https://orcid.org/0000-0001-6100-1654