My content object A has attributes 'cost' & 'tax' - Decimal (from decimal). I try: A.cost + A.tax ---> security error '+' method for Decimal-class. I solve problem by 'zope.proxy.removeAllProxies' , but i think it's bad. What other ways are exist? i get Zope3 from trunk and not find 'decimal'-package in 'zope/app/globalmodules.zcml'. Why?