The whole “Type manipulation” section has nothing to do with this issue, but at the same time is the usual source of complexity in type definitions. Even worse,

The whole “Type manipulation” section has nothing to do with this issue, but at the same time is the usual source of complexity in type definitions. Even worse, it serves as a clever challenge for people to make such dynamic interfaces well-typed, instead of making it boring, autogenerated once and then discouraged.