FAMILIES OF GRAPH-DIFFERENT HAMILTON PATHS

Let D subset of N be an arbitrary subset of the natural numbers. For every n, let M(n, D) be the maximum of the cardinality of a set of Hamiltonian paths in the complete graph K-n such that the union of any two paths from the family contains a not necessarily induced cycle of some length from D. We determine or bound the asymptotics of M(n, D) in various special cases. This problem is closely related to that of the permutation capacity of graphs and constitutes a further extension of the problem area around Shannon capacity. We also discuss how to generalize our cycle-difference problems and present an example where cycles are replaced by 4-cliques. These problems are in a natural duality to those of graph intersection, initiated by Erdos, Simonovits, and Sos. The lack of kernel structure as a natural candidate for optimum makes our problems quite challenging.