anchor.diff:           onMain { main.EnterHeader.Text <- "" } >>.
            let item = {IsCompleted = Stream.Var.create false
                        Header = Stream.Var.create header}
  -         (Stream.Var.get itemsVar @ [item])
  +         Stream.Var.get itemsVar @ [item]
            |> Stream.Var.set itemsVar)
   
         changedCompleted
  
positive.code: 
  [<AutoOpen>]
  module internal Util =
    let setupWhen (onEvent: IEvent<_, _>) =
      let mainCtx = ivar ()
      let handler =
  
negative.code: 
        let itemsVar = Stream.Var.create []
  
        let changedCompleted =
          Stream.Var.tap itemsVar
          |> Stream.switchMap (fun items ->
             Stream.ofSeq items
             |> Stream.mergeMap (fun item -> Stream.Var.tap item.IsCompleted)
             |> Stream.mapConst items)
          |> Stream.merge (Stream.Var.tap itemsVar)
  
        let itemsAndCtrls =
          Stream.Var.tap itemsVar
          |> Stream.scanFromJob [] (fun oldItemsAndCtrls newItems -> onMain {
             let newCtrl item =
               let ctrl = ToDo.UI.ItemControl ()
  