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Acta Mathematica Scientia > 2014 > 34 > 3 > 639-652
Journal of Mathematical Analysis and Applications > 2011 > 374 > 1 > 201-209
Acta Mathematica Scientia > 2014 > 34 > 3 > 639-652
Journal of Mathematical Analysis and Applications > 2011 > 374 > 1 > 201-209