A closed interval is an interval that includes all of its limit points. If the endpoints of the interval are finite numbers and , then the interval is denoted . If one of the endpoints is , then the interval still contains all of its limit points (although not all of its endpoints), so and are also closed intervals, as is the interval .
See alsoClosed Ball, Closed Disk, Closed Set, Half-Closed Interval, Interval, Limit Point, Open Interval
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ReferencesCroft, H. T.; Falconer, K. J.; and Guy, R. K. Unsolved Problems in Geometry. New York: Springer-Verlag, p. 1, 1991.Gemignani, M. C. Elementary Topology. New York: Dover, 1990.
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Weisstein, Eric W. "Closed Interval." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/ClosedInterval.html