Zhendong Shao Roger K. Yeh David Zhang The <i>L</i>(2, 1)-labeling on the skew and converse skew products of graphs. 59-64 2007 20 Appl. Math. Lett. 1 http://dx.doi.org/10.1016/j.aml.2006.02.032 db/journals/appml/appml20.html#ShaoYZ07