anchor.diff:  
       let [<Fact>] iterativeFrpCyclicWorks () =
           let world = World.makeDefault ()
  -        let world = World.createEntity typeof<EntityDispatcher>.Name None (Some Jim.EntityName) Simulants.DefaultGroup world |> snd
  -        let world = World.createEntity typeof<EntityDispatcher>.Name None (Some Bob.EntityName) Simulants.DefaultGroup world |> snd
  +        let world = World.createEntity typeof<EntityDispatcher>.Name None (Some Jim.EntityName) DefaultGroup world |> snd
  +        let world = World.createEntity typeof<EntityDispatcher>.Name None (Some Bob.EntityName) DefaultGroup world |> snd
           let world = !-- Bob.Visible --> Jim.Visible ^ world
           let world = !-- Jim.Visible -/> Bob.Visible ^ world
           let world = Bob.SetVisible false world
  
positive.code: open Prime
  open Prime.Stream
  open Nu
  module WorldTests =
  
      let TestFilePath = "TestFile.nugame"
      let StringEvent = stoa<string> "String/Event"
      let Jim = Simulants.DefaultGroup => "Jim"
      let Bob = Simulants.DefaultGroup => "Bob"
  
      let [<Fact>] runOneFrameThenCleanUp () =
          let world = World.makeEmpty ()
  
negative.code:     let [<Fact>] entitySubscribeWorks () =
          let world = World.makeDefault ()
          let handleEvent = fun evt world -> (Cascade, World.updateUserState (fun _ -> evt.Subscriber) world)
          let world = World.subscribe handleEvent StringEvent DefaultEntity world
          let world = World.publish String.Empty StringEvent EventTrace.empty Game world
          Assert.Equal<Simulant> (DefaultEntity :> Simulant, World.getUserState world)
  
      let [<Fact>] gameSerializationWorks () =
          let world = World.makeDefault ()
          let oldWorld = world
          World.writeGameToFile TestFilePath world
          let world = World.readGameFromFile TestFilePath world
          Assert.Equal<Name> (DefaultScreen.GetName oldWorld, DefaultScreen.GetName world)
          Assert.Equal<Name> (DefaultGroup.GetName oldWorld, DefaultGroup.GetName world)
          Assert.Equal<Name> (DefaultEntity.GetName oldWorld, DefaultEntity.GetName world)
  
      let [<Fact>] iterativeFrpWorks () =
          let world = World.makeDefault ()
          let world = World.createEntity typeof<EntityDispatcher>.Name None (Some Jim.EntityName) DefaultGroup world |> snd
          let world = World.createEntity typeof<EntityDispatcher>.Name None (Some Bob.EntityName) DefaultGroup world |> snd
          let world = !-- Bob.Visible --- map not --> Jim.Visible ^ world
          let world = Bob.SetVisible false world
          Assert.False (Bob.GetVisible world)
  