anchor.diff:              let lensSeq = lens |> Lens.map sieve |> Lens.mapWorld unfold
               let lenses = Lens.explodeIndexedOpt indexOpt lensSeq
               let subscription = fun _ world ->
  +                let previous =
  +                    match World.tryGetKeyedValue<PartialComparable<Guid, int * Lens<obj, World>> Set> guid world with
  +                    | Some previous -> previous
  +                    | None -> Set.empty
                   let mutable current = Set.empty
                   let mutable count = Lens.get lensSeq world |> Seq.length
                   let mutable enr = lenses.GetEnumerator ()
  
positive.code:                 let added = Set.difference current previous
                  let removed = Set.difference previous current
                  let changed = Set.notEmpty added || Set.notEmpty removed
                  previous <- current
                  let world =
                      if changed then
                          let world =
  
negative.code:             (origin : ContentOrigin)
              (parent : Simulant)
              world =
              let guid = Gen.id
              let sieve' = fun a ->
                  match lens.PayloadOpt with
  