anchor.diff:               collection.Add v |> ignore
           ) |> ignore
   
  -//        let mutable result = 0
  -//        let resultCb = derived |>  Mod.unsafeRegisterCallbackKeepDisposable (fun v ->
  -//            result <- v
  -//        )
  +        let mutable result = 0
  +        let resultCb = derived |>  Mod.unsafeRegisterCallbackKeepDisposable (fun v ->
  +            result <- v
  +        )
   
           let mutable r = 0
           let puller = System.Threading.Thread(ThreadStart(fun _ ->
  
positive.code:                 r <- derived |> Mod.force
          ))
  
          puller.Start()
          middle.Start()
          inputThread.Start()
  
negative.code:         
  
      [<Test>]
      let ``[Mod] fan out, different eval strategy``() =
  
          let input = Mod.init 10
  
          let middle = input |> Mod.map id
          let outputA = middle |> Mod.map id
          let outputB = middle |> Mod.map id
          let mutable marked = false
          outputB.AddMarkingCallback(fun () -> marked <- true) |> ignore
  
          outputA |> Mod.force |> should equal 10
          marked |> should equal true
  
  
      [<Test>]
      let ``[Mod] mod concurrency test super crazy callbacks``() =
          
          let pulledValues = List<int>()
  