anchor.diff:  
       /// The screen type that allows transitioning to and from other screens, and also hosts the
       /// currently interactive layers of entities.
  +    /// TODO: make this into a class with address checking in the constructor.
       and [<CustomEquality; NoComparison>] Screen =
           { ScreenAddress : Screen Address }
       
  
positive.code:     /// to implement things like buttons, characters, blocks, and things of that sort.
      /// OPTIMIZATION: Includes pre-constructed entity change and update event addresses to avoid
      /// reconstructing new ones for each entity every frame.
      and [<CustomEquality; NoComparison>] Entity =
          { mutable EntityStateOpt : EntityState
            EntityAddress : Entity Address
  
negative.code:             end
      
      /// The game type that hosts the various screens used to navigate through a game.
      /// TODO: make this into a class with address checking in the constructor.
      and [<CustomEquality; NoComparison>] Game =
          { GameAddress : Game Address }
      
  