December2015 Cs Q43
0. Which of the following statements is false?
- A
Top-down parsers are LL parsers where first L stands for left - to - right scan and second L stands for a leftmost derivation.
- B
(000)* is a regular expression that matches only strings containing an odd number of zeroes, including the empty string.
- C
Bottom-up parsers are in the LR family, where L stands for left - to - right scan and R stands for rightmost derivation.
- D
The class of context - free languages is closed under reversal. That is, if L is any context - free language, then the language LR = {wR: w∈L} is context - free.
- Option : B
- Explanation :
- Top-down parsers are LL parsers where first L stands for left - to - right scan and second L stands for a leftmost derivation.Correct
- (000)* is a regular expression that matches only strings containing an odd number of zeroes, including the empty string.Incorrect (000)* will generate ε, 000, 000000, 000000000, ........ multiples of 3 which include odd and even strings, so this is incorrect.
- Bottom-up parsers are in the LR family, where L stands for left - to - right scan and R stands for rightmost derivation.Correct
- The class of context - free languages is closed under reversal. That is, if L is any context - free language, then the language LR = {wR: w∈L} is context - free.Correct
So, option (B) is correct.
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