This code results in the following error: cycle.boo(4,28): BCE0071: Inheritance cycle detected: 'IController'. DefaultController implements IController for DefaultLayout. -----------------[code] internal interface IController: def Execute() as string internal interface ILayout(IController): def Add(child as IController) class DefaultLayout(DefaultController, ILayout): def Add(child as IController): pass override def Execute() as ArrayList: pass class DefaultController(IController): virtual def Execute() as ArrayList: _layout.Add(self) return _layout.Execute()