anchor.diff:      _successor = successor;
     }
   
  -  void processRequest(PurchaseRequest request);
  +  void processRequest(PurchaseRequest request) {
  +    if (_successor != null) {
  +      _successor.processRequest(request);
  +    }
  +  }
   }
   
   class ManagerPurchasePower extends PurchasePower {
  
positive.code:   void processRequest(PurchaseRequest request) {
      if (request.amount < _allowable) {
        print("President will approve $request");
      }
      else {
        print("Your request for $request needs a board meeting!");
      }
    }
  }
  
  
negative.code:   void processRequest(PurchaseRequest request) {
      if (request.amount < _allowable) {
        print("Director will approve $request");
        return;
      }
      super.processRequest(request);
    }
  }
  
  