if (log.isDebugEnabled()) log.debug("Adding parent " + parent);
    Set findParents(Frame child, String relation_prototype)    {	HashSet results = new HashSet();	synchronized (kb) {	    Iterator itr = kb.values().iterator();	    while (itr.hasNext()) {		Frame relationship = (Frame) itr.next();		if (descendsFrom(relationship, relation_prototype)) {		    Frame c = getRelate(relationship,					child_proto_slot, 					child_slot_slot,					child_value_slot);		    if ( c != null && c.equals(child)) {			Frame parent = getRelate(relationship,						parent_proto_slot, 						parent_slot_slot,						parent_value_slot);			if (parent != null) results.add(parent);		    }		    		}	    }	}	return results;    }