Hi, What we need for Pharo4 wrt to Slots is just finishing the PropertySlot example. Not much to do here. -> remove base slot when removing the last propertySlot -> when adding a PropertySlot higher in the hierarchy, move base slot up. To do this, we of course need #removeSlot: , which is ready to be reviewed here: https://pharo.fogbugz.com/f/cases/15095/add-removeSlot-to-ClassDescription (there are after many simplifications possible, e.g. rewrite #removeInstVarNamed: to use this, but this is for Pharo5) Marcus