25 May 2001 / Invited article, in "Theoretical Methods for Strongly Correlated Electrons", D. Senechal, A.-M. Tremblay, and C. Bourbonnais Eds., CRM Series in Mathematical Physics (Springer, New York, 2003)
7 Oct 2001 / in "Theoretical Methods for Strongly Correlated Electrons", p. 341, Eds. David Sénéchal, André-Marie Tremblay, Claude Bourbonnais (Springer-Verlag, New-York, 2004)