*/
  @SafeVarargs
  public static <B> Set<List<B>> cartesianProduct(Set<? extends B>... sets) {
    return cartesianProduct(asList(sets));
  }

  private static final class CartesianSet<E> extends ForwardingCollection<List<E>>
      implements Set<List<E>> {
    private final transient ImmutableList<ImmutableSet<E>> axes;
    private final transient CartesianList<E> delegate;