1. How many rings can share a quaternary atom?
2. Topological stereochemistry
3. (b) in Chemical Applications of Graph Theory (Ed.: ), Academic Press, London, 1976, Chapter 2;
4. (c) in Graph Theory and Topology in Chemistry (Eds.: ), Elsevier, Amsterdam, 1987, p. 43.
5. (a) Aspekte von Kraftfeldrechnungen, Wolfgang Baur, München, 1981, Chapter 4.6.3;