[1] Griggs J R, Yeh R K. Labeling graphs with a condition at distance two [J]. SIAM J Discrete Math, 1992, 5(4): 586-595.
[2] Hale W K. Frequency assignment: theorem and applications [J]. Proceedings of the IEEE, 1980, 68(12): 1497-1514.
[3] Georges J P, Mauro D W. Generalized vertex labelings with a condition at distance two [J]. Congr Numer, 1995, 109: 141-159.
[4] Chang G J, Kuo D. The L(2, 1)-labeling on graphs [J]. SIAM J Discrete Math, 1996, 9(2): 309-316.
[5] Georges J P, Mauro D W, Whittlesey M. Relating path covering to vertex labelings with a condition at distance two [J]. Discrete Math, 1994, 135(1/2/3): 103-111.
[6] Whittlesey M, Georges J P, Mauro D W. On the λ-number of Qn and related graphs [J]. SIAM J Discrete Math, 1995, 8(4): 499-506.
[7] Chang G J, Ke W T, Kuo D, et al. On L(d, 1)-labelings of graphs [J]. Discrete Math, 2000, 220(1/2/3): 57-66.
[8] Georges J P, Mauro D W, Stein M I. Labeling products of complete graphs with a condition at distance two [J]. SIAM J Discrete Math, 2000, 14(1): 28-35.
[9] Jin X T, Yeh R K. Graph distance-dependent labeling related to code assignment in computer networks [J]. Naval Research Logistics, 2005, 52(2): 159-164.
[10] Yeh R K. The edge span of distance two labelings of graphs [J]. Taiwanese J Math, 2000, 4(3): 397-405.
[11] Feng Guizhen, Song Zengmin. Edge span of L(d, 1)-labeling on some graphs [J]. Journal of Southeast University: English Edition, 2005, 21(1): 111-114.
[12] Niu Qingjie, Lin Wensong, Song Zengmin. L(s, t)edge spans of trees and product of two paths [J]. Journal of Southeast University: English Edition, 2007, 23(4): 639-642.
[13] Griggs J R, Jin X T. Real number graph labelings with distance conditions [J]. SIAM J Discrete Math, 2006, 20(2): 302-327.
[14] Griggs J R, Jin X T. Real number channel assignments for lattices [J]. SIAM J Discrete Math, 2008, 22(3): 996-1021.