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Tomasz Górecki
Faculty of Mathematics and Computer Science,
Adam Mickiewicz University, Uniwersytetu Poznańskiego 4Poznań, Poland
Mirosław Krzyśko
Interfaculty Institute of Mathematics and Statistics
The President Stanisław Wojciechowski State University of Applied Sciences in KaliszKalisz, Poland
Waldemar Wołyński
Faculty of Mathematics and Computer Science,
Adam Mickiewicz University, Uniwersytetu Poznańskiego 4Poznań, Poland