Published Online: Dec 22, 2018
Page range: 277 - 286
DOI: https://doi.org/10.2478/mgrsd-1984-010132
© 2018 Wiktor Grygorenko, published by Sciendo
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License.
Wiktor Grygorenko