1. Metric ternary distributive semi-lattices;Avann;Proc. Amer. Math. Soc.,1961
2. Medians in median graphs;Bandelt;Discrete Appl. Math.,1984
3. Median algebras;Bandelt;Discrete Math.,1983
4. Graphes et Hypergraphes;Berge,1970
5. Categories for the Working Mathematician;Maclane,1971