anchor.diff:                         }
               let rec scanNoTimeout () =
                   async { match x.scanArrivals(f) with
  -                        |   None -> let! ok = waitOneNoTimeout
  +                        |   None -> let! ok = waitOne(Timeout.Infinite)
                                       if ok then
                                           return! scanNoTimeout()
                                       else
  
positive.code:     [<AutoSerializable(false)>]
      [<CompiledName("FSharpMailboxProcessor`1")>]
      type MailboxProcessor<'Msg>(initial, ?cancellationToken) =
          let cancellationToken = defaultArg cancellationToken Async.DefaultCancellationToken
          let mailbox = new Mailbox<'Msg>()
          let mutable defaultTimeout = Threading.Timeout.Infinite
          let mutable started = false
          let errorEvent = new Event<System.Exception>()
  
negative.code: 
      [<Sealed>]
      [<AutoSerializable(false)>]        
      type Mailbox<'Msg>(cancellationSupported: bool) =  
          let mutable inboxStore  = null 
          let mutable arrivals = new Queue<'Msg>()
          let syncRoot = arrivals
  