anchor.diff:  /// An Ecs system with just a single component.
   and [<AbstractClass>] SystemSingleton<'t, 'w when 't : struct and 't :> Component> (comp : 't) =
       inherit System<'w> ()
  +
       let mutable comp = comp
  +
       member this.Component with get () = &comp
  +
       type 'w Ecs with
  +
           member this.IndexSingleton<'t, 'w when 't : struct and 't :> Component> systemName =
               let systemOpt = this.TryIndexSystem<SystemSingleton<'t, 'w>> systemName 
               if Option.isNone systemOpt then failwith ("Could not find expected system '" + systemName + "'.")
  
positive.code:     member this.QualifyMultiplexed multiId entityId =
          if this.QualifyCorrelated entityId then
              let comp = this.IndexCorrelated entityId
              comp.Entries.ContainsKey multiId
          else false
  
      member this.IndexMultiplexed multiId entityId =
          let componentMultiplexed = &this.IndexCorrelated entityId
          componentMultiplexed.Entries.[multiId]
  
      member this.RegisterMultiplexed multiId entityId comp ecs =
          let _ = this.RegisterCorrelated entityId ecs
  
negative.code: 
      member this.Components
          with get () = components
  
      member this.FreeIndex
          with get () = freeIndex
  
  