* theory of computing question

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Question: Suppose that a certain programming language permits only identifiers that begin with a letter, contain at least one but no more than three digits, and can have any number of letters. Give a grammar and an accepter for such a set of identifiers. EXAMPLE PROBLEM (use as hint) While passwords generally have few restrictions, they are normally not totally free. Suppose that in a certain system passwords can be of arbitrary length, but must contain at least one letter : a - z and one number 0 - 9. Construct a grammar that generates the set of such legal passwords. Answer: =rest>letter>rest>1>rest>rest>>abc>123456789