anchor.diff:                      let lens' = enr.Current
                       match lens'.Get world with
                       | Some (index, _) -> 
  -                        let guid = Gen.idDeterministic index guid
  +                        let guid = Gen.idDeterministic index expansionId
                           let lens'' = { Lens.dereference lens' with Validate = fun world -> Option.isSome (lens'.Get world) } --> snd
                           let item = PartialComparable.make guid (index, lens'')
                           current <- Set.add item current
                           count <- count - 1
                       | None -> ()
                   let previous =
  -                    match World.tryGetKeyedValue<PartialComparable<Guid, int * Lens<obj, World>> Set> guid2 world with
  +                    match World.tryGetKeyedValue<PartialComparable<Guid, int * Lens<obj, World>> Set> previousSetKey world with
                       | Some previous -> previous
                       | None -> Set.empty
                   let added = Set.difference current previous
                   let removed = Set.difference previous current
                   let changed = Set.notEmpty added || Set.notEmpty removed
  -                let world = World.addKeyedValue guid2 current world
  +                let world = World.addKeyedValue previousSetKey current world
                   let world =
                       if changed then
                           let world =
  
positive.code:             (origin : ContentOrigin)
              (parent : Simulant)
              world =
              let guid = Gen.id
              let guid2 = Gen.id
              let sieve' = fun a ->
                  match lens.PayloadOpt with
                  | Some payload ->
  
negative.code:                 //while enr.MoveNext () do
                  //    let item = enr.Current
                  //    let index = match indexOpt with Some indexer -> indexer item | None -> i
                  //    let expansionIdDet = Gen.idDeterministic index expansionId
                  //    let lensOpt = lenses |> Seq.item index
                  //    let lensItem = { Lens.dereference lensOpt with Validate = fun world -> Option.isSome (lensOpt.Get world) } --> snd
                  //    current <- Set.add (PartialComparable.make expansionIdDet (index, lensItem)) current
                  //    i <- i + 1
                  let items = Lens.get lensSeq world
                  let mutable current = Set.empty
  