docs: public static <T1, T2, R> Single<R> zip(Single<? extends T1> single, BiFunction<? super T1, ? super T2, ? extends R> fn,
              Publisher<? extends T2> app) {
          Single<R> res = Single.fromPublisher(Future.fromPublisher(single.toFlowable()).zip(fn,app));
          return res;
      }