(a to b) is open interval .
(a+ to b-) is open interval .
(a+ to b) is half open interval .
(a to b-) is half open interval .
For example
>> 3+ 3 >> 3- 3 >> 3 to 5 [3, 5] >> 3+ to 5- (3, 5) >> 3 to 5- [3, 5)