1. D. Bauer, H. J. Broersma, H. J. Veldman, Not every 2-tough graph is hamiltonian
2. A method in graph theory;Bondy;Discrete Math.,1976
3. S. Brandt, O. Favaron, Z. Ryjáček, Closure and stable hamiltonian properties in claw-free graphs
4. A note onK4;Broersma;Discrete Math.,1993
5. Closure concepts for claw-free graphs;Broersma;Discrete Math.,1998