A Traceability Conjecture for Oriented Graphs

A (di)graph G of order n is k-traceable (for some k, 1 ≤ k ≤ n) if every induced sub(di)graph of G of order k is traceable. It follows from Dirac’s degree condition for hamiltonicity that for k ≥ 2 every k-traceable graph of order at least 2k − 1 is hamiltonian. The same is true for strong oriented graphs when k = 2, 3, 4, but not when k ≥ 5. However, we conjecture that for k ≥ 2 every k-traceable oriented graph of order at least 2k − 1 is traceable. The truth of this conjecture would imply the truth of an important special case of the Path Partition Conjecture for Oriented Graphs. In this paper we show the conjecture is true for k ≤ 5 and for certain classes of graphs. In addition we show that every strong k-traceable oriented graph of order at least 6k − 20 is traceable. We also characterize those graphs for which all walkable orientations are k-traceable.