class ArraySet {
    private static Object[] a;
    public  static int size;

    /*:
      public static ghost specvar init :: bool;

      public static specvar content :: objset;
      vardefs
        "content == {n. EX j. n = a.[j] & 0 <= j & j < size}";

      invariant "init --> a ~= null & 0 < a..Array.length & 
          0 <= size & size <= a..Array.length";

    */

    public static void initialize() 
    /*:
      modifies init, content
      ensures "init & content = {}";
    */
    {
        a = new /*: hidden */ Object[100];
        size = 0;
        //: init := "True";
    }


    public static boolean contains(Object x)
    /*:
      requires "init & x ~= null"
      ensures "result = (x : content)";
     */
    {
        int i = 0;
        while (i < size) {
            if (a[i] == x) {
                return true;
            } else {
                i = i + 1;
            }
        }
        return false;
    }

}