public static IObservable <bool> WhenBusy(this ICanBeBusy busy)
 {
     return(busy.WhenAnyValue(x => x.IsBusy));
 }
 public static IObservable <bool> WhenNotBusy(this ICanBeBusy busy)
 {
     return(busy.WhenAnyValue(x => x.IsBusy).Select(x => !x));
 }