1. Anderberg, M.R.: Cluster analysis for applications, (Academic Press 1973)
2. Tou, J.T., and Gonzalez, R.C.: ‘Pattern recognition principles’, Pattern classification by distance functions, (Addison Wesley 1974),Chap. 3,
3. Tryon, R.C., and Bailey, D.E.: Cluster analysis, (McGraw-Hill, New York 1970)