anchor.diff:                      | (true, correlation) -> correlation.Add systemName
                       | (false, _) -> this.Correlations.Add (entityId, List [systemName])
               | None -> failwith ("Could not find expected system '" + systemName + "'.")
  -                
   
   /// An Ecs system that explicitly associates components by entity id.
   type [<AbstractClass>] SystemJunctioned<'t, 'w when 't : struct and 't :> Component> (junctionedSystemNames : string array) =
  
positive.code:         Seq.fold
              (fun world (_, system : 'w System) -> system.ProcessActualize this world)
              world systemsOrdered
  
  /// An Ecs system with just a single component.
  and [<AbstractClass>] SystemSingleton<'t, 'w when 't : struct and 't :> Component> (comp : 't) =
  
negative.code:             subsystems |>
              Seq.map (fun entry -> Task.Run (fun () ->
                  let system = entry.Value
                  do system.RegisterPipedValue ecs
                  let _ = system.ProcessActualize ecs Unchecked.defaultof<'w>
                  (entry.Key, system.IndexPipedValue ecs)) |> Vsync.AwaitTaskT) |>
              Vsync.Parallel |>
              Vsync.RunSynchronously |>
              dictPlus
  