Sarah Spence Adams Matthew Tesch Denise Sakai Troxell Bradford Westgate Cody Wheeland On the hole index of L(2, 1)-labelings of r-regular graphs. 2391-2393 2007 155 Discrete Applied Mathematics 17 http://dx.doi.org/10.1016/j.dam.2007.07.009 db/journals/dam/dam155.html#AdamsTTWW07