anchor.diff:      member this.System5 = system5
       member this.System6 = system6
       member this.System7 = system7
  +    member this.Cached = cache.Keys
  +    member this.Allocated = allocated.AsReadOnly ()
   
       member this.Contains entityId =
           cache.ContainsKey entityId
  
positive.code:     member this.NextEntityId world =
          let world =
              if unallocated.Count = 0
              then this.Preallocate Constants.Ecs.PreallocateAmount world
              else world
          let entityIdInv = Seq.head unallocated
          let entityId = UInt64.MaxValue - entityIdInv
  
negative.code:         let struct (unregistered3, world) = ecs.UnregisterCorrelated<'c3> entityId world
          struct (unregistered || unregistered2 || unregistered3, world)
  
      member this.Expand count world =
          let mutable world = world
          for _ in 0 .. count - 1 do
              let entityId = Gen.id64
  