public static void main(String[] args)
    {
        // --- Initialize 4 lists with the same data.  ---
        int[] array1 = {5, 2, 21, 1, 9, 4, 12, 7, 3, 10, 6};
        ArrayList<Integer> list1 = new ArrayList<>();
        ArrayList<Integer> list2 = new ArrayList<>();
        ArrayList<Integer> list3 = new ArrayList<>();
        ArrayList<Integer> list4 = new ArrayList<>();
        for ( int i : array1 )
        {
            list1.add(i);
            list2.add(i);
            list3.add(i);
            list4.add(i);
        }

        // --- Test for mystery1  ---
        System.out.println("Original List 1 (for mystery1): " + list1);
        mystery1(list1);
        System.out.println("Final List 1 (after mystery1):   " + list1);
        System.out.println("----------------------------------------");
        
        // --- Test for mystery2 ---
        System.out.println("Original List 2 (for mystery2): " + list2);
        mystery2(list2);
        System.out.println("Final List 2 (after mystery2):   " + list2);
        System.out.println("----------------------------------------");
        
        // --- Test for mystery3 ---
        System.out.println("Original List 3 (for mystery3): " + list3);
        mystery3(list3);
        System.out.println("Final List 3 (after mystery3):   " + list3);
        System.out.println("----------------------------------------");
        
        // --- Test for mystery4 ---
        System.out.println("Original List 4 (for mystery4): " + list4);
        mystery4(list4);
        System.out.println("Final List 4 (after mystery4):   " + list4);
    }