import edu.neu.ccs.demeter.dj.*; Container = List. List : N | E. E = . N = Item List. Item = Ident Weight. Weight = int. SummingVisitorDJ = int extends Visitor. CountingVisitorDJ = int extends Visitor. AverageVisitorDJ = CountingVisitorDJ SummingVisitorDJ float extends Visitor. ResultVisitorDJ = AverageVisitorDJ extends Visitor. Main = .