anchor.diff:              return! loop status
             | Running ->
               let workers = [ 1 .. count ] |> List.map (fun _ -> newWorker self)
  -            workers |> List.iter (fun worker -> worker.Post(Worker.Do(command)))
  +            workers |> List.iter (fun worker -> worker.Post(Worker.Do(command)); worker.Post(Retire))
               return! loop status
           | Manager.Stop ->
             return! loop Stopped
  
positive.code:       async {
          let! msg = self.Receive ()
          match msg with
          | Worker.Do command ->
            match command with
            | Process uri -> doit uri
  
negative.code: 
  type Worker =
    | Do of Command
    | Retire
  
  type Manager =
    | Do of int * Command
  