return ImmutableList.copyOf(elements);
  }

  public void testCartesianProduct_binary1x1() {
    assertThat(cartesianProduct(list(1), list(2))).contains(list(1, 2));
  }

  public void testCartesianProduct_binary1x2() {
    assertThat(cartesianProduct(list(1), list(2, 3)))
        .containsExactly(list(1, 2), list(1, 3))
        .inOrder();
  }

  public void testCartesianProduct_binary2x2() {