Ciao, i have a class with some instance variable. For example a class Product with some instance variable and the = method set to: = anItem anItem ifNil:[^false]. anItem class = self class ifFalse:[ ^false]. ^ rfrConsegna = anItem rfrConsegna and:[ rfrSubTable = anItem rfrSubTable and:[ rfrDcm = anItem rfrDcm and:[ indexRiga = anItem indexRiga and:[ referenceTime = anItem referenceTime and:[ consumer = anItem consumer and:[ item = anItem item and:[ opzioniVoce = anItem opzioniVoce ]]]]]]] Some of these variables are instances of classes with specific implementation and some variables themselves. I set the relative hash method to: hash ^ rfrConsegna hash bitXor:( rfrSubTable hash bitXor: ( rfrDcm hash bitXor: ( indexRiga hash bitXor: ( referenceTime hash bitXor: ( consumer hash bitXor: ( item hash bitXor: ( opzioniVoce hash ))))))) Now my doubt, having many variables affecting the hash calculation, is to be sure that different instances don't give the same hash value. Some advice about it? Thanks, Dario