Module with basic infrastructure for function inheritance based on open rercusion.

See the work of William Cook.

We use the following terminology.

• A closed function is an ordinary function.
• A mixin function is an open function that can be inherited from, or that extends another open function.

We obtain a closed function from a base mixin base and a number of mixin extensions e1,...,en as follows:

 mixin (en <@> ... <@> e1 <@> base)