public static <T> void check_postings_list_equal(pnode_t<T> a, pnode_t<T> b) {
    while (a != null && b != null) {
      System.out.print(a.data + " ");
      assert(a.data == b.data);
      assert(a.jump == null &&
              b.jump == null ||
             (a.jump != null && b.jump != null && a.jump.data == b.jump.data));
      if (a.jump != null) {
        System.out.print(a.jump.data);
      }
      System.out.println("");
      a = a.next; b = b.next;
    }

    assert(a == null &&
           b == null);
  }