Which of the following grammar rules violate the requirements of an operator grammar ? P, Q, R are nonterminals, and r, s, t are terminals.

1.    P → Q R                    
2.    P → Q s R
3.    P → ε       
4.    P → Q t R r 

(A) 1 only
(B) 1 and 3 only
(C) 2 and 3 only
(D) 3 and 4 only


Answer: (B)

Explanation: See Question 4 of http://www.geeksforgeeks.org/compilers-set-1/.

Operator grammar should not have two or more variables in its production side by side, and should not have null productions.

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