Guillermo De Ita Luna Polynomial Classes of Boolean Formulas for Computing the Degree of Belief. 430-440 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3315&spage=430 2004 conf/iberamia/2004 IBERAMIA db/conf/iberamia/iberamia2004.html#Luna04