D Recurrences

[Timon Gehr]

Timon Gehr wrote:
> Steve Schveighoffer wrote:
>> On Thu, 09 Jun 2011 14:45:49 -0400, Andrej Mitrovic
>> <andrej.mitrovich at 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