code: public static <E> ImmutableSet<E> of(E e1, E e2, E e3, E e4) {
      return construct(4, 4, e1, e2, e3, e4);
    }
docs: Returns an immutable set containing the given elements, minus duplicates, in the order each was
  first specified. That is, if multiple elements are {@linkplain Object#equals equal}, all except
  the first are ignored.