中国科学院数学与系统科学研究院期刊网
A Note on L(2, 1)-labelling of Trees
Ming-qing ZHAI, Chang-hong LU, Jin-long SHU
Acta Mathematicae Applicatae Sinica(English Series) . 2012, (2): 395 -400 .  DOI: 10.1007/s10255-012-0151-9