public static IDisposable Subscribe <T>(this IParallelObservable <T> value, Action <T> onNext)
        {
            ParallelObserver <T> observer = new ParallelObserver <T>(onNext);
            IDisposable          subject  = value.Subscribe(observer);

            return(subject);
        }
        public static IDisposable Subscribe <T>(this IParallelObservable <T> value, Action <T> onNext, Action <Exception> onError, Action onCompleted)
        {
            ParallelObserver <T> observer = new ParallelObserver <T>(onNext, onError, onCompleted);
            IDisposable          subject  = value.Subscribe(observer);

            return(subject);
        }