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D. Luo
Department of Mathematics,
Guizhou UniversityGuiyang
J. R. Wang
Department of Mathematics,
Guizhou UniversityGuiyang
M. Fečkan
Department of Mathematical Analysis and Numerical Mathematics, Faculty of Mathematics, Physics and Informatics,
Comenius University in Bratislava,
Mathematical Institute of Slovak Academy of Sciences,
Bratislava,Bratislava