Chapter 13.1, Problem 31E

Give production rules in Backus-Naur form for an identifier if it can consist of

a) one or more lower case letters.

b) at least three but no more than six lowercase letters.

c) one to six uppercase or lowercase letters beginning with an uppercase letter,

d) a lowercase letter, followed by a digit or an underscore, followed by three or four alphanumeric characters (lower or uppercase letters and digits).