async await reactive options

Simple.cs

    class Program
    {
        static void Main(string[] args)
        {
            var inputs = new[] {1,2,3};

            // ensures next task isn't executed until prior is completed - which is the implication with
            // subscribe based async code
            inputs.ToObservable().
                Select((i) => Observable.Defer(() => LongishTask(i).ToObservable())).
                Concat().
                Subscribe(_ => { }, (e) => Console.WriteLine($" Exception {e.Message}"));

            Console.ReadLine();

            // will run more than one task at once, but error will be surfaced correctly
            inputs.ToObservable().
                SelectMany( async (i) => await LongishTask(i)).
                Subscribe(_ => { }, (e) => Console.WriteLine($" Exception {e.Message}"));

            Console.ReadLine();

            // execution will take place concurrently for each task, but exception when raised
            // won't surface in the pipeline, but rather take down the program instead
            inputs.ToObservable().
                Subscribe(async v => await LongishTask(v), (e) => Console.WriteLine($" Exception {e.Message}"));

            Console.ReadLine();
        }

        static async Task<bool> LongishTask(int index)
        {
            Console.WriteLine($"I've started {index}");

            // adjust to get even items to take less time than odd ones 
            await Task.Delay((index & 1) == 0 ? 250: 1000);

            // just throw an exception and see what happens
            if (index == 3)
            {
                throw new ArgumentException("");

            }
            Console.WriteLine($"I've finished {index}");
            return true;
        }
    }