anchor.diff:              (origin : ContentOrigin)
               (parent : Simulant)
               world =
  -            let guid = Gen.id
  -            let guid2 = Gen.id
  +            let expansionId = Gen.id
  +            let previousSetKey = Gen.id
               let sieve' = fun a ->
                   match lens.PayloadOpt with
                   | Some payload ->
  
positive.code:             let lensSeq = lens |> Lens.map sieve |> Lens.mapWorld unfold
              let lenses = Lens.explodeIndexedOpt indexOpt lensSeq
              let subscription = fun _ world ->
                  //let items = Lens.get lensSeq world
                  //let mutable current = Set.empty
                  //let mutable enr = items.GetEnumerator ()
  
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
  