A closed interval is an interval that includes all of its limit points. If the endpoints of the interval are finite numbers a and b, then the interval {x:a<=x<=b} is denoted [a, b]. If one of the endpoints is ± ∞, then the interval still contains all of its limit points (although not all of its endpoints), so [a, ∞) and (-∞, b] are also closed intervals, as is the interval (-∞, ∞).

closed ball | closed disk | closed set | half-closed interval | interval | limit point | open interval