// Erika Wolfe, CSE 143
// A collection that contains no duplicate elements.
public interface Set<E> {
    // want to have: add, size, contains, remove, isEmpty
    
    // Adds the given value to this set only if it isn't 
    // already contained in the set
    public void add(E val);
    
    // Returns the number of elements in this set
    public int size();
    
    // Returns true if the set has no elements, false otherwise.
    public boolean isEmpty();
    
    // Returns true if the given value is an element of this set,
    // false otherwise
    public boolean contains(E val);
    
    // Removes the given value from this set only if it is 
    // already contained in the set.
    public void remove(E val);
}