anchor.diff:                  r <- derived |> Mod.force
           ))
   
  +
           puller.Start()
           middle.Start()
           inputThread.Start()
  
positive.code: 
          //collection.Count |> should equal 0
          printfn "awaited"
          //result |> should equal currentValue
          derived |> Mod.force |> should equal currentValue
          printfn "done"
  
  
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>()
  