1. Hamiltonian cycles in regular graphs;Bollobás,1978
2. Some theorems on abstract graphs;Dirac,1952
3. P. Erdös and A. M. Hobbs, Hamilton cycles in regular graphs of moderate degree, J. Combinatorial Theory Ser. B, in press.
4. R. Häggkvist, personal communication.
5. unsolved problem;Häggkvist,1976