If an interval is closed, can it be unbounded?

1 Answer
May 1, 2018

No.

Explanation:

A closed interval necessarily includes the endpoints, such as #[1, 2]#.

If either of the ends of the interval is infinite, we know that we have to write it as open (or half closed), such as #[1, infty) or (-infty, infty)#.

This means that an unbounded (i.e. including #pm infty#) cannot be closed.