ABSTRACT
To close out our discussion of the basic properties of the real numbers, we remind the reader of an especially convenient type of subset of R, and one that will be extremely useful to us in our further development of analysis. Recall that an interval I ⊂ R is the set of all real numbers lying between two specified real numbers a and b where a < b. The numbers a and b are called the endpoints of the interval I . There are three types of intervals in R:
1. Closed. Both endpoints are included in the interval, in which case we denote the interval as I = [a, b ].
