@CheckReturnValue
    @NonNull
    public final <R> ParallelFlowable<R> reduce(@NonNull Callable<R> initialSupplier, @NonNull BiFunction<R, ? super T, R> reducer) {
        ObjectHelper.requireNonNull(initialSupplier, "initialSupplier");
        ObjectHelper.requireNonNull(reducer, "reducer");
        return RxJavaPlugins.onAssembly(new ParallelReduce<T, R>(this, initialSupplier, reducer));
    }