ISRO | ISRO CS 2013 | Question 6
Which of the following productions eliminate left recursion in the
productions given below:
S → Aa | b
A → Ac | Sd | ε
(A) S → Aa | b
A → bdA’
A’ → A’c | A’ba | A | ε
(B) S → Aa | b
A → A’ | bdA’,
A’ → cA’ | adA’ | ε
(C) S → Aa | b
A → A’c | A’d
A’ → bdA’ | cA | ε
(D) S → Aa | b
A → cA’ | adA’ | bdA’
A’ → A | ε
Answer: (B)
Explanation:
To remove left recursion from the grammar of the form : A → Aα | β We rewrite the production rules as: A → βA' A'→ αA'| ε Given Grammar: S → Aa | b A → Ac | Sd | ε after finding indirect left recursion, grammar: S → Aa | b A → Ac | Aad | bd | ε here, α = c, ad, β = bd So, Grammar after removing left recursion = S → Aa | b A → A' | bdA' A'→ CA'| ada'| ε
So, option (B) is correct.
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