'First class' Relationships

Currently reading an article, "First Class Relationships in an Object-
oriented Language", by Gavin Bierman and Alisdair Wren:
http://homepages.inf.ed.ac.uk/wadler/fool/program/final/4/4_Paper.pdf

Found in the "Lambda the Ultimate" blog:
http://lambda-the-ultimate.org/node/2013

Maybe it can be done in Python too, with a metaclass "Relationship".
The relation can probably be added dynamically to an object/class.
Some typecheek can be added too, if necessary.

Bye,
bearophile

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