anchor.diff:                      | None -> world
                   | None -> world)
                   world removed
  -                
  +
           static member internal addSynchronizedSimulants mapper monitorMapper simulantMapId added origin owner parent world =
               Seq.fold (fun world keyAndLens ->
                   let (key, lens) = PartialComparable.unmake keyAndLens
  
positive.code:             let monitorMapper =
                  fun a _ world ->
                      let b =
                          if refEq a.Value monitorResult || genEq a.Value monitorResult then
                              match sieveResultOpt with
                              | Some b -> b
                              | None -> sieve (lens.Get world)
                          else sieve (lens.Get world)
                      monitorResult <- a.Value
                      sieveResultOpt <- Some b
  
negative.code: 
  namespace Nu
  open System
  open Prime
  open Nu
  
  