Interval
From AoPSWiki
Definition
An interval is a range of values. The most common uses of an interval are for domain and range.
Symbols
If an interval has either ( or ) on it, the values at the end are NOT included.
If an interval has either [ or ] on it, the values at the end ARE included.
Note: 
and 
are generally not included as endpoints.
Examples
- (2,3) means all real values between 2 and 3, but not including 2 and 3
- [-2,0) means all real values between -2 and 0, but does not include 0
