@article{BMMS_2014_37_4_a21,
     author = {Zhao Chang-Jian and Wing-Sum Cheung},
     title = {On {Opial-Dan's} {Type} {Inequalities}},
     journal = {Bulletin of the Malaysian Mathematical Society},
     year = {2014},
     volume = {37},
     number = {4},
     url = {http://geodesic.mathdoc.fr/item/BMMS_2014_37_4_a21/}
}