The H0 function (Global Hubness) is a new index to measure the quantity of the topological information of any a-directed graph.
 Massimo Buscema, Auto Contractive Maps, Semeion Technical Paper 32, Aracne Publisher 2008, Rome, ISBN 978–88–548–1714–2.
 Massimo Buscema and Pier L. Sacco, Auto-contractive Maps, the H Function, and the Maximally Regular Graph (MRG): A New Methodology for Data Mining, in V. Capecchi et al. (eds.), Applications of Mathematics in Models, Artificial Neural Networks and Arts, Chapter 11, DOI 10.1007/978-90-481-8581-8_11, Springer Science+Business Media B.V. 2010).