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Journal of Mathematics and Applications > 2014 > Vol. 37 > 111--118
Demonstratio Mathematica > 2007 > Vol. 40, nr 3 > 559-566
Journal of Mathematics and Applications > 2014 > Vol. 37 > 111--118
Demonstratio Mathematica > 2007 > Vol. 40, nr 3 > 559-566