anchor.diff:  
       member this.IndexSystem<'s when 's :> 'w System> systemName =
           this.TryIndexSystem<'s> systemName |> Option.get
  +
  +    member this.ProcessUpdate world =
  +        Seq.fold
  +            (fun world (_, system : 'w System) -> system.ProcessUpdate this world)
  +            world systemsOrdered
  +
  +    member this.ProcessPostUpdate world =
  +        Seq.fold
  +            (fun world (_, system : 'w System) -> system.ProcessPostUpdate this world)
  +            world systemsOrdered
  +
  +    member this.ProcessActualize world =
  +        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) =
  
positive.code:     let systemsUnordered = dictPlus [] : Dictionary<string, 'w System>
      let systemsOrdered = List () : (string * 'w System) List
      let correlations = dictPlus [] : Dictionary<Guid, string List>
  
      member internal this.Correlations 
          with get () = correlations
  
      member this.ProcessUpdate world =
          Seq.fold
              (fun world (_, system : 'w System) -> system.ProcessUpdate this world)
              world systemsOrdered
  
      member this.ProcessPostUpdate world =
          Seq.fold
              (fun world (_, system : 'w System) -> system.ProcessPostUpdate this world)
              world systemsOrdered
  
      member this.ProcessActualize world =
          Seq.fold
              (fun world (_, system : 'w System) -> system.ProcessActualize this world)
              world systemsOrdered
  
      member this.RegisterSystem systemName system =
          systemsUnordered.Add (systemName, system)
  
negative.code: 
  namespace Nu
  open System
  open System.Collections.Generic
  open System.IO
  open System.Threading
  open System.Threading.Tasks
  open Prime
  
  /// The base component type of an Ecs.
  