Selectmany

Observable.SelectMany()
Observable.SelectMany<TSource, TResult>(IObservable<TSource>, Func<TSource, IObservable<TResult>>, Func<Exception, IObservable<TResult>>, Func<IObservable<TResult>>)
Qbservable.SelectMany()
Qbservable.SelectMany<TSource, TCollection, TResult>(IQbservable<TSource>, Expression<Func<TSource, IObservable<TCollection>>>, Expression<Func<TSource, TCollection, TResult>>)