Suppose that a PL permits only identifiers that begin with a letter, contain at least one but not more than three digits, and can have any number of letters.

(a) Give a BNF grammar for such a set of identifiers. Assume the following productions for letters and digits:

--> a|b|c|...|z

--> 0|1|2|...|9

(b) Draw a parse tree for the identifier: ab32