anchor.diff:          else struct (false, world)
   
       interface Query<'w> with
  -
           override this.Correlation = correlation
  -
  -        override this.Filter entityId =
  -            let indexOpt = system.TryIndexCorrelatedToI entityId
  -            if indexOpt > -1 then
  -                cache.[entityId] <- indexOpt
  -                true
  -            else
  -                cache.Remove entityId |> ignore<bool>
  -                false
  +        override this.Filter entityId = system.TryIndexCorrelatedToI entityId > -1
   
   /// An ECS query.
   type Query<'c, 'c2, 'w when
  
positive.code: type Query<'c, 'w when
      'c : struct and 'c :> 'c Component> (ecs : 'w Ecs) =
  
      let cache = OrderedDictionary<uint64, int> HashIdentity.Structural
      let correlation = hashSetPlus<string> StringComparer.Ordinal [typeof<'c>.Name]
      let system = ecs.IndexSystem<'c, SystemCorrelated<'c, 'w>> ()
      let unallocated = HashSet<uint64> HashIdentity.Structural
  
negative.code:     member this.System = system
  
      member this.Iterate (fn : Statement<'c, 's>) state =
          let mutable world = state
          let array = system.Correlateds.Array
          for i in 0 .. array.Length - 1 do
              world <- fn.Invoke (&array.[i], world)
          world
  
      member this.IterateBuffered (fn : Statement<'c, 'w>) world =
          system.WithCorrelatedsBuffered (fun aref world ->
              let mutable world = world
              let array = aref.Array
              for i in 0 .. array.Length - 1 do
                  world <- fn.Invoke (&array.[i], world)
              world)
              world
  
      member this.Index (entityId : uint64) (fn : Statement<'c, 's>) state =
          let cref = system.IndexCorrelated entityId
          fn.Invoke (&cref.Index, state)
  
      member this.IndexBuffered (entityId : uint64) (fn : Statement<'c, 'w>) world =
          system.WithCorrelatedsBuffered (fun array state ->
              let index = system.IndexCorrelatedToI entityId
              fn.Invoke (&array.[index], state))
              world
  
      member this.RegisterCorrelated ordered comp entityId world =
  