## Quick Reference

A number defining one end of an interval on the real line. Each of the finite intervals [*a*, *b*], (*a*, *b*), [*a*, *b*) and (*a*, *b*] has two end-points, *a* and *b*. Each of the infinite intervals [*a*, ∞), (*a*, ∞), (−∞, *a*] and (−∞, *a*) has one end-point, *a*.

*Subjects:*
Mathematics.