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: /// perf benefits of data-orientation. Really, this functionality is here for flexibility and convenience more than
  /// anything else (which is good enough in almost all cases where multi-components are used).
  type [<NoEquality; NoComparison; Struct>] ComponentMultiplexed<'t when 't : struct> =
      internal
          { mutable RefCount : int
            Entries : Dictionary<Guid, 't Simplex> }
      interface Component with
          member this.RefCount
              with get () = this.RefCount
              and set value = this.RefCount <- value
      member this.Components
          with get () = this.Entries.Values :> 't Simplex IEnumerable
      member this.RegisterMultiplexed (multiId, comp) =
          this.Entries.Add (multiId, { Simplex = comp })
      member this.UnregisterMultiplexed multiId =
          this.Entries.Remove multiId
  
  /// A base system type of an Ecs.
  type [<AbstractClass>] 'w System () =
  
negative.code:     member this.QualifyMultiplexed multiId entityId =
          if this.QualifyCorrelated entityId then
              let comp = this.IndexCorrelated entityId
              comp.Simplexes.ContainsKey multiId
          else false
  
      member this.IndexMultiplexed multiId entityId =
          let componentMultiplexed = &this.IndexCorrelated entityId
          componentMultiplexed.Simplexes.[multiId]
  
      member this.RegisterMultiplexed multiId entityId comp ecs =
          let _ = this.RegisterCorrelated entityId ecs
  