Yet another extension method to combine two observable collections, this time we have IObservable<T>.Concat which is very similar to IObservable<T>.Merge, but crucially, when you concatenate one observable collection to another, the subscription to the second observable…

The IObservable<T>.CombineLatest extension method is very similar to IObservable<T>.Zip and IObservable<T>.Merge in that it combines two observable collections and returns a new one.