The "raison d'etre" of hierarchical dustering theory stems from one basic phe- nomenon: This is the notorious non-transitivity of similarity relations. In spite of the fact that very often two objects may be quite similar to a third without being that similar to each other, one still wants to dassify objects according to their similarity. This should be achieved by grouping them into a hierarchy of non-overlapping dusters such that any two objects in ne duster appear to be more related to each other than they are to objects outside this duster. In everyday life, as well as in essentially...