anchor.diff:                  | None -> failwith ("Could not find expected system '" + systemName + "'.")
   
   /// An Ecs system with components stored by entity id.
  -type SystemCorrelated<'c, 'w when 'c : struct and 'c :> 'c Component and 'w :> Freezable> (compacting, reserve, name) =
  +type SystemCorrelated<'c, 'w when 'c : struct and 'c :> 'c Component and 'w :> Freezable> (ordered, reserve, name) =
       inherit SystemMany<'w> (name)
   
       let systemNames = Unchecked.defaultof<'c>.SystemNames
  
positive.code:     let correlations = dictPlus [] : Dictionary<Guid, int>
      let correlationsBack = dictPlus [] : Dictionary<int, Guid>
  
      new (compacting, reserve) = SystemCorrelated (compacting, reserve, typeof<'c>.Name)
      new (reserve) = SystemCorrelated (false, reserve, typeof<'c>.Name)
      new () = SystemCorrelated (false, Constants.Ecs.ArrayReserve, typeof<'c>.Name)
  
  
negative.code:                     | (false, _) -> this.Correlations.Add (entityId, List [systemName])
              | _ -> failwith ("Could not find expected system '" + systemName + "'.")
  
  type SystemHierarchical<'c, 'w when 'c : struct and 'c :> 'c Component and 'w :> Freezable> (ordered, reserve, name) =
      inherit System<'w> (name)
  
      let systemTree = ListTree.makeEmpty<SystemCorrelated<'c, 'w>> ()
      let systemDict = dictPlus [] : Dictionary<Guid, SystemCorrelated<'c, 'w>>
  
      new (ordered, reserve) = SystemHierarchical (ordered, reserve, typeof<'c>.Name)
      new (reserve) = SystemHierarchical (false, reserve, typeof<'c>.Name)
      new () = SystemHierarchical (false, Constants.Ecs.ArrayReserve, typeof<'c>.Name)
  
  