Published Online: Dec 22, 2018
Page range: 171 - 180
DOI: https://doi.org/10.2478/mgrsd-1988-030120
© 2018 Zdzisław Mikulski, published by Sciendo
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License.
Zdzisław Mikulski