Funding for this research was provided by:
Ministry of National Education, Poland (510-18-09, 510-18-54)
Text and Data Mining valid from 2019-01-10
Received: 20 August 2018
Revised: 14 December 2018
Accepted: 18 December 2018
First Online: 10 January 2019
Compliance with ethical standards
: The authors declare that they have no conflict of interest.
: This article does not contain any studies with human participants or animals performed by the author.