anchor.diff:  open Aardvark.Base
   open Aardvark.Base.Incremental.AListReaders
   
  -[<CompiledName("ChangeableListKey")>]
  +[<CompiledName("ChangeableListKey"); AllowNullLiteral>]
   type clistkey internal (t : Time) =
       member internal x.Time = t
   
  
positive.code:     member x.Clear() =
          clear()
  
      interface System.Collections.IEnumerable with
          member x.GetEnumerator() =
              (content.Values :> System.Collections.IEnumerable).GetEnumerator()
  
negative.code:             if r.IsIncremental then r.Emit deltas
              else r.Reset content
  
      member x.Find(item : 'a) =
          let t = content |> Seq.tryPick (fun (t,v) -> if Object.Equals(v,item) then Some t else None)
          match t with
              | Some t -> clistkey t
              | None -> null
  
      interface System.Collections.IEnumerable with
          member x.GetEnumerator() =
              (content.Values :> System.Collections.IEnumerable).GetEnumerator()
  