Roberto Fern ndez and Aldo Procacci
Cluster expansion for abstract polymer models. New bounds from an old approach
(44K, LaTeX)

ABSTRACT.  We revisit the classical approach to cluster expansions, based on 
 tree graphs, and establish a new convergence 
 condition that improves those by Koteck\'y-Preiss and 
 Dobrushin, as we show in some examples. The strategy is to 
 better exploit a well known tree-graph expression, due to Penrose.