Vietnam Journal of Mathematics
Vietnam Journal of Mathematics > 2017 > 45 > 4 > 575-584
Vietnam Journal of Mathematics > 2017 > 45 > 4 > 713-719
Vietnam Journal of Mathematics > 2017 > 45 > 4 > 681-694
Vietnam Journal of Mathematics > 2017 > 45 > 4 > 651-668
Vietnam Journal of Mathematics > 2017 > 45 > 4 > 737-746