1. , and , A generalization of Ore's theorem involving neighborhood unions. University of Twente preprint.
2. , , and , Neighborhood unions and a generalization of Dirac's Theorem. Preprint.
3. Neighborhood unions and hamiltonian properties in graphs
4. and , Neighborhood intersections and a generalizations of Ore's Theorem. Proceedings of the 2nd International Conference on Graph Theory, San Francisco (1989), to appear.