Giovanni Lagorio Marco Servetto Elena Zucca Featherweight Jigsaw: A Minimal Core Calculus for Modular Composition of Classes. 244-268 2009 ECOOP http://dx.doi.org/10.1007/978-3-642-03013-0_12 conf/ecoop/2009 db/conf/ecoop/ecoop2009.html#LagorioSZ09