anchor.diff:        Stream.MVar.tap modelMVar
         |> Stream.mapFun (fun model ->
            not (Map.isEmpty model) && Map.forall (fun _ -> isCompleted) model)
  +      |> Stream.keepPreceding1
         |> Stream.subscribeJob (fun allCompleted -> onMain {
            main.CompleteAll.IsChecked <- Nullable<bool> allCompleted })
   
  
positive.code:           (Stream.ofObservableOnMain control.MouseEnter |> Stream.mapConst +1)
            (Stream.ofObservableOnMain control.MouseLeave |> Stream.mapConst -1)
          |> Stream.scanFromFun 0 (+)
          |> Stream.subscribeJob (fun n -> onMain {
             control.Remove.Visibility <-
               if 0 < n then Visibility.Visible else Visibility.Hidden })
  
negative.code:               |> ignore) })
  
        Stream.MVar.tap modelMVar
        |> Stream.keepPreceding1
        |> Stream.subscribeJob (fun model -> onMain {
           let n = Map.toSeq model |> Seq.filter (snd >> isActive) |> Seq.length
           main.NumberOfItems.Text <- sprintf "%d items left" n })
  
        Stream.MVar.tap modelMVar
        |> Stream.keepPreceding1
        |> Stream.subscribeJob (fun model -> onMain {
           let n = Map.toSeq model |> Seq.filter (snd >> isCompleted) |> Seq.length
           main.ClearCompleted.Visibility <-
  