On Jul 4, 8:14 pm, Steven D'Aprano <[EMAIL PROTECTED]> wrote: > However, there's a very subtle flaw in the idea. While "the intersection" > of two sets is well-defined, "these two sets intersect" is (surprisingly!) > _not_ well-defined.
Poppycock! It's perfectly well defined: two sets intersect if and only if their intersection is nonempty. There's absolutely no reason to single out the empty set for special treatment in this definition. > The problem comes if we (perhaps naively) try to say that if a set A is a > subset of set B, set A must intersect with B. Well of course false statements are going to cause problems. > (Not all intersecting sets are subsets, but all subsets are intersecting > sets.) Not true. > As a result, any proposed function or method that returns a True/False > value for whether set A intersects with set B needs to define (and > justify) what it means to say that two sets intersect when one or both are > the empty set. Nope. There's one, obvious, correct definition, as given above. No need to mention the empty set at all. Richard -- http://mail.python.org/mailman/listinfo/python-list
