code: public static <E> Iterable<E> unionIterable(Iterable<Iterable<E>> its) {
  	return new ImmutableCompoundIterable<Iterable<E>,E>
  	    (its,
  	     new IdFunction<Iterable<E>>());
      }
docs: Returns an immutable <code>Iterable</code> that is the union
  of several <code>Iterable</code>s (in the order thet are given
  in <code>its</code>).