Errata

Abstract

Volume 7, number 2, page 182

In the diagram —— d _UV —— should replace —— d _uv —— and the equation below it should read

$d_{UV}=\frac{1}{n_U}\sum _{u\hspace{0.17em}\in \hspace{0.17em}U}\left(\frac{1}{n_V}\sum _{\upsilon \in V}{d}_{u\upsilon }\right),$