anchor.diff:              let system = this.Ecs.IndexSystem<'c, SystemCorrelated<'c, 'w>> ()
               let system2 = this.Ecs.IndexSystem<'c2, SystemCorrelated<'c2, 'w>> ()
               let system3 = this.Ecs.IndexSystem<'c3, SystemCorrelated<'c3, 'w>> ()
  -            for kvp in this.Cache do
  -                let entityId = kvp.Key
  +            for entityId in this.Cache do
                   fn
                       (system.IndexCorrelated entityId)
                       (system2.IndexCorrelated entityId)
  
positive.code: /// An ECS query.
  and [<AbstractClass>] 'w Query (filter : (string HashSet -> bool), ecs : 'w Ecs) =
  
      let cache = dictPlus<Guid, 'w EntityRef> HashIdentity.Structural []
  
      abstract Correlation : string HashSet
      member this.Ecs = ecs
  
negative.code:         | (true, correlation) ->
              correlation.Add this.Name |> ignore<bool>
              ecs.CorrelationChanges.[entityId] <- correlation
              ecs.FilterForQueries this.Name correlation entityId
          | (false, _) ->
              let correlation = HashSet.singleton StringComparer.Ordinal this.Name
              ecs.Correlations.Add (entityId, correlation)
              ecs.CorrelationChanges.[entityId] <- ecs.EmptyCorrelation
              ecs.FilterForQueries this.Name correlation entityId
  
          // fin
          componentMultiplexed
  