anchor.diff:                  elif KeyboardState.isKeyDown KeyboardKey.Up then msg (Face Upward)
                   elif KeyboardState.isKeyDown KeyboardKey.Down then msg (Face Downward)
                   else msg Nil
  -             entity.UpdateEvent => msg SynchronizeBounds
  +             entity.UpdateEvent => msg Update
  +             entity.Parent.PostUpdateEvent => msg SynchronizeBounds
                entity.Parent.PostUpdateEvent => msg PostUpdate
  -             entity.Parent.PostUpdateEvent => msg SynchronizeBounds
                entity.CollisionEvent =|> fun evt -> msg (Collision evt.Data)
                entity.SeparationEvent =|> fun evt -> msg (Separation evt.Data)]
   
  
positive.code:                 just avatar
  
              | SynchronizeBounds ->
                  
                  // synchronize bounds
                  let avatar = Avatar.updateBounds (constant (entity.GetBounds world)) avatar
                  just avatar
  
negative.code:              entity.BodyShape == bodyShapes]
  
          override this.Channel (_, entity) =
              [entity.UpdateEvent => msg SynchronizeBounds
               entity.UpdateEvent =|> fun _ ->
                  let force = v2Zero
                  let force = if KeyboardState.isKeyDown KeyboardKey.Right then v2 Constants.Field.WalkForce 0.0f + force else force
  