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    CS 1992 Q 2 xii. For a context-free grammar, FOLLOW(A) is the set of terminals that can appear immediately to the right of non-terminal A in some "sentential" form. We define two sets LFOLLOW(A) and RFOLLOW(A) by replacing the word "sentential" by "left sentential" and "right most sentential" respectively in the definition of FOLLOW(A). 

Which of the following statements is/are true? 

(a) FOLLOW(A) and FOLLOW (A) maybe different. 
(b) FOLLOW(A) and FOLLOW (A) are always the same. 
(c) Al the three sets are identical. 
(d) Al the three sets are different. 

please explain ! 

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balu Senior Member Joined: 20Feb2007 Online Status: Offline Posts: 236	Topic: Q on CC Posted: 22Feb2007 at 2:21pm
	CS 1992 Q 2 xii. For a context-free grammar, FOLLOW(A) is the set of terminals that can appear immediately to the right of non-terminal A in some "sentential" form. We define two sets LFOLLOW(A) and RFOLLOW(A) by replacing the word "sentential" by "left sentential" and "right most sentential" respectively in the definition of FOLLOW(A). Which of the following statements is/are true? (a) FOLLOW(A) and FOLLOW (A) maybe different. (b) FOLLOW(A) and FOLLOW (A) are always the same. (c) Al the three sets are identical. (d) Al the three sets are different. please explain ! Post Resume: Click here to Upload your Resume & Apply for Jobs

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manju Senior Member Joined: 20Feb2007 Online Status: Offline Posts: 221	Posted: 22Feb2007 at 2:24pm
	Consider G as E -> +ET / T T -> TF / F F -> (E) / id When we find FOLLOW (E) We apply rules: 1. If it is start smbl, add $ 2. If A -> (alpha) B (beta), add (FIRST of beta) - epsilon 3. If A -> (alpha) OR (alpha) B (beta) with epsilon, add FOLLOW (A) So, FOLLOW (T) = FIRST (F) = (, id......... rule 2 FOLLOW (T) = FOLLOW (E) = $ .... rule 3 Does rule 2 implies RFOLLOW, while rule 3 implies LFOLLOW?? Coz considering parse tree, rules seem to apply for Left and right sentensial. i.e. in string, like id id..... , rule 2 gives RFOLLOW set while in strings like + id id, rule 3 gives end of string i.e. LFOLLOW set... seems confusing... still i think, whtever i wrote is somewhr related... though m nt so sure..
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