5 ms·
It's just unfortunate terminology -- a closed set is one whose complement is open, not one which is not open.
by akalin 5y ago
It's just unfortunate terminology -- a closed set is one whose complement is open, not one which is not open.
- prof-dr-ir 5y agoIndeed. Sets are not doors, as the saying goes, because they can be open and closed at the same time.