class MultiFlatMapIterable implements Multi<R> {

    @Override
    public void subscribe(Flow.Subscriber<? super R> subscriber) {
        source.subscribe(new FlatMapIterableSubscriber<>(subscriber, mapper, prefetch));
    }

      MultiFlatMapIterable(Multi<T> source,
                         Function<? super T, ? extends Iterable<? extends R>> mapper,
                         int prefetch);

}