## Intervals and Directed Numbers

Directed numbers indicate an inequality to be satisfied on the number line. The inequality may be

1. A closed interval, likewritten aswith the endpoints 1 and 2 included as possible values ofThe inclusion of the endpoints is indicated by black circles.

2. An open interval, likewritten aswith the endpoints -3 and 4 excluded as possible values ofThe exclusion of the endpoints is indicate by white circles.

3. A half open interval, likewritten aswith the endpoints -2 excluded and 2 included, respectively, as possible values ofIncluded points are indicated by back circles and excluded points by white circles.

4. One sided inequalities likeorThese are unbounded. Included points are indicated by back circles and excluded points by white circles. That the inequality is one sided is indicated by an arrow at one end.