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Advances in Difference Equations > 2013 > 2013 > 1 > 1-10
Journal of Mathematics and Applications > 2010 > Vol. 32 > 109-116
Journal of Mathematics and Applications > 2009 > Vol. 31 > 99-106
Demonstratio Mathematica > 2008 > Vol. 41, nr 4 > 813-822
Demonstratio Mathematica > 2008 > Vol. 41, nr 4 > 823-832