# Problem We love our phones. Each phone has a number. The phone number or BSU's CS Department can be expressed in these, human-readable ways: * +1(208)426-5640 * (208)426-5640 * 426-5640 Of course, you only key-in the digits. As described in lecture, give a regular definition for the regular language of human-readable phone numbers, like those above. Give a well-structured regular definition, with named parts, not just a regular expression. Use only the basic regular-expression operators described in lecture: alternation, concatenation, and repetition (i.e., Kleene star). Your answer does not have to be perfect, or express only "callable" numbers. Also, don't worry about weird numbers, like 911. # Process The regular expression operators which are allowed include: * `a|b` - Alternation. * `ab` - Concatenation. * `a*` - Repetition (zero or more repeating). In lecture, there was an example regular definition given for the regular language of numbers in Pascal. > [!example] Example of a regular definition for the regular language of numbers in Pascal > ``` > digit 0|1|2|3|4|5|6|7|8|9 > integer digit digit* > fraction (. integer)|^ > exponent ((e|E)(+|-|^) integer)|^ > number integer fraction exponent > ``` ``` digit 0|1|2|3|4|5|6|7|8|9 digits digit digit* country \+ digits phone country* \( segment \) ``` # Answer ...