anchor.diff:                              then res
                               else Packed(vrt, true)                        
                       else
  -                        let fs = f cur.First false
  +                        let fs = f cur.First false (List.append been [cur])
                           match fs with
                           | Packed(pckd, is) ->
                               if is
  
positive.code:             | :? IntermidiateNode as cur ->
                  if List.contains current been
                  then
                      Others(Intermidiate(cur), false, (cur.Slot, cur.Extension))
                  else
                      been <- List.append been [cur]
                      if cur.Others = Unchecked.defaultof<_>
                      then
                          let res = f cur.First true
                          match res with
                          | Others(_, _, _) ->
                              res
  
negative.code:                                         cur.Others.RemoveAt i
                                          cur.Others.Insert(i,pckd)
                          Others (Intermidiate(cur), true, (cur.Slot, cur.Extension))
          f tree.Root false [] |> ignore
          tree