public void testCartesianProduct_unary() {
    assertThat(cartesianProduct(set(1, 2))).containsExactly(list(1), list(2));
  }

  public void testCartesianProduct_binary0x0() {
    Set<Integer> mt = emptySet();
    assertEmpty(cartesianProduct(mt, mt));
  }

  public void testCartesianProduct_binary0x1() {
    Set<Integer> mt = emptySet();