refinement<E>
    Element is E

    List[Element] is SingleLinkedList<E> {
        make: --> List[Element]
        is
        SingleLinkedList();
        
        addFirst: List[Element] e:Element --> List[Element]
        is
        void addFirst(E e);

        getFirst: List[Element] -->? Element
        is
        E getFirst();
        
        removeFirst: List[Element] -->?List[Element]
        is
        void removeFirst();
        
        isEmpty: List[Element]
        is
        boolean isEmpty();

        getLast: List[Element] -->? Element is E getLast();
        
        removeLast: List[Element] -->? List[Element]
        is
        void removeLast();
        
        addLast: List[Element] e:Element --> List[Element]
        is
        void addLast(E e);
        
        size: List[Element] --> int
        is
        int size();
        
        get: List[Element] index:int -->? Element 
        is
        E get(int index);
        
        set: List[Element] index:int e:Element -->? List[Element] 
        is
        void set(int index, E e);
        
        add: List[Element] index:int e:Element -->? List[Element] 
        is
        void add(int index, E e);
        
        remove: List[Element] index:int -->? List[Element] 
        is
        void remove(int index);
    }
end refinement