Chapter 12.1, Problem 37ES

To determine

Write a regular expression to define the given set of strings. Use the shorthand notations given in the section when ever convenient. In most cases, your expression will describe other strings in addition to the given ones. but try to make your answer fit the given strings as closely as possible wïthin reasonable space limitations.

All United States social security numbers (which consist of three digits. a hyphen, two digits, another hyphen, and finally four more digits), wtiere the final four digits start with $a3$ and end with $a6$.