Tim Peters writes: > [Ethan Furman <et...@stoneleaf.us>] > > .. on the other hand, it seems that collections of related flags > > are often treated as in set theory, where the empty set is a > > member of any non-empty set. > > Not how any set theory I've ever seen works: a set S contains the > empty set if and only if some member of S _is_ the empty set. Which > is also how Python's frozenset.__contains__ works (a plain Python set > can never contain the empty set, because only a frozenset can contain > a set (empty or not)).
Maybe Ethan's thinking of one of the standard set-theoretic constructions of natural numbers? Ie, 0 = {}, 1 = {0} = {{}}, 2 = {0, 1} = {{}, {{}}}, etc. Steve _______________________________________________ Python-Dev mailing list -- python-dev@python.org To unsubscribe send an email to python-dev-le...@python.org https://mail.python.org/mailman3/lists/python-dev.python.org/ Message archived at https://mail.python.org/archives/list/python-dev@python.org/message/XDCKP55FVS6CLVUYJMQF5BF5HA4TZOK4/ Code of Conduct: http://python.org/psf/codeofconduct/