## Interval

A collection of points on a Line Segment. If the endpoints and are Finite and are included, the interval is called Closed and is denoted . If one of the endpoints is , then the interval still contains all of its Limit Points, so and are also closed intervals. If the endpoints are not included, the interval is called Open and denoted . If one endpoint is included but not the other, the interval is denoted or and is called a Half-Closed (or Half-Open) interval.