Martyna, Agnieszka
Gäbler, Hans-Eike
Bahr, Andreas
Zadora, Grzegorz
Article History
Received: 29 November 2017
Revised: 26 February 2018
Accepted: 5 March 2018
First Online: 17 April 2018
Compliance with ethical standards
: The authors declare that they have no conflict of interest.