Relation vr = new Relation (other, localField, remoteField, direction, subnodesAreProperties);
Relation vr = makeClone ();
    public Relation getGroupbyPropertyRelation () {	if (groupby == null)	    throw new RuntimeException ("getGroupbyPropertyRelation called on non-group-by relation");	Relation vr = new Relation (other, localField, remoteField, direction, subnodesAreProperties);	vr.order = order;	vr.prototype = groupbyprototype;	return vr;    }