}

  public void testCartesianProduct_binary0x1() {
    Set<Integer> mt = emptySet();
    assertEmpty(cartesianProduct(mt, set(1)));
  }

  public void testCartesianProduct_binary1x0() {
    Set<Integer> mt = emptySet();
    assertEmpty(cartesianProduct(set(1), mt));
  }

  private static void assertEmpty(Set<? extends List<?>> set) {
    assertTrue(set.isEmpty());