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Open Mathematics > 2017 > 15 > 1 > 331-339
Annales UMCS, Mathematica > 2013 > 67 > 2 > 53-58
Annales Polonici Mathematici > 1991-1992 > 56 > 3 > 227-232
Open Mathematics > 2017 > 15 > 1 > 331-339
Annales UMCS, Mathematica > 2013 > 67 > 2 > 53-58
Annales Polonici Mathematici > 1991-1992 > 56 > 3 > 227-232