1. S.M. Allen and N. Dunkin, Frequency assignment problems: representations and solutions, Technical report, University of Glamorgan, 1997.
2. S.M. Allen, D.H. Smith and S. Hurley, Lower bounding techniques for frequency assignment, Discrete Mathematics
197/198 (1999) 41–52.
3. G. Ausiello, P. Crescenzi, G. Gambosi, V. Kann, A. Marchetti-Spaccamela and M. Protasi, Complexity and Approximation, Springer, 1999.
4. F. Barasi and J. van den Heuvel, Graph labelling, acyclic orientations, and greedy algorithms, manuscript, 2001.
5. M. Bernstein, N.J.A. Sloan and P.E. Wright, On sublattices of the hexagonal lattice, Discrete Mathematics
170 (1997) 29–39.