Timon Gehr wrote: > Steve Schveighoffer wrote: >> On Thu, 09 Jun 2011 14:45:49 -0400, Andrej Mitrovic >> <andrej.mitrov...@gmail.com> wrote: >> >> > I never understood why it's called "open" interval. What does it 'open'? >> >> Look at the terminology section of >> http://en.wikipedia.org/wiki/Interval_(mathematics) >> >> No clue as to the "why" :) >> >> -Steve > > Actually it does not make too much sense to use the terms open or closed on > integer intervals in a strict mathematical sense. If your universe is the > integers, all subsets of the integers are neither open nor closed, with the > exception of the empty set and the set of all integers, which are both open > > and > closed. :o)
I'm sorry, this was misinformation. Actually *all* subsets are both open and closed. Timon