How to Subscribe with lambda instead of IDisposable

[martinrhan]

In the documentation, there are examples that when calling Subsribe function, lambdas are passed in as arguments. However, I only have IObservable.Subscribe(IObserver) in my IDE. What extension namespace should I include? The examples in documentation didn't provide that information.

[anaisbetts]

This is an Rx.NET question, but it's probably in either System,System.Reactive, or System.Reactive.Linq