The L(2, 1, 1)-labellings of caterpillars. - Xiaoling Zhang 010; Kecai Deng (Int. J. Comput. Math. Comput. Syst. Theory, 2016)

Characterization results for L(2, 1, 1)-labeling problem on trees. - Kecai Deng; Xiaoling Zhang 010 (Discuss. Math. Graph Theory, 2017)

Distance two labelings in regular bipartite graphs. - Xiaoling Zhang 010; Kecai Deng (Ars Comb., 2018)