anchor.diff:                      //printfn "%A tried to pull from level %A but has level %A" top.Id level top.Level
                       // all greater pulls would be from the future
                       raise <| LevelChangedException(this, this.Level, depth - 1)
  -                                                                     
  -                res <- r
  -
  -
  +                        
  +                let caller = token.Caller
                   if not (isNull caller) then
                       if this.Reevaluate then
                           caller.Reevaluate <- true
  
positive.code:             let arr = handles.Array
              if myIndexOf(arr, value, count) >= 0 then
                  false
              elif count = 8 then
                  let set = HashSet arr
                  set.Add(value) |> ignore
                  handles.Set <- set
                  mode <- 2uy
                  count <- 9
                  true
              else
                  arr.[count] <- value
  
negative.code: open System.Threading
  open System.Linq
  open System.Runtime.InteropServices
  
  [<AutoOpen>]
  module VolatileCollection = 
      [<Literal>]
      let SetThreshold = 8
  
  [<AllowNullLiteral>]
  type IWeakable<'a when 'a : not struct> =
  