Andrea Asperti Luca Padovani Claudio Sacerdoti Coen Irene Schena HELM and the Semantic Math-Web. 59-74 2001 conf/tphol/2001 TPHOLs http://link.springer.de/link/service/series/0558/bibs/2152/21520059.htm db/conf/tphol/tphol2001.html#AspertiPCS01