gistfile1.cs

public IObservable<IObservable<T>> Window(
        this IObservable<T> source,
        // An Observable that fires when Windows should open
        IObservable<TWindowOpening> windowOpenings,
        // A Func that given a Window opening, will determine when that window
        // should close.
        Func<TWindowOpening, IObservable<TWindowClosing>> windowClosingSelector);