# Theory Of Computation MCQ - Context free languages

51:

If a language is denoted by a regular expression
L = ( x )* (x | y x ) ,
then which of the following is not a legal string within L ?

 A. yx B. xyx C. x D. x y x y x Option: D Explanation :
52:

If every string of a language can be determined, whether it is legal or illegal in finite time, the language is called

 A. decidable B. undecidable C. interpretive D. non-deterministic Option: A Explanation :
53:

The defining language for developing a formalism in which language definitions can be stated, is called

 A. syntactic meta language B. decidable language C. intermediate language D. high level language Option: A Explanation :
54:

If L be set of strings from alphabet, then kleen closure of L is given as

 A. $\tiny \dpi{120} L^{+}=\bigcup_{i=0}^{.}L^{i}$ B. $\tiny \dpi{120} L_{0}=\bigcup_{i=0}^{.}L^{i}$ C. $\tiny \dpi{120} L^{*}=\bigcup_{i=0}^{\infty }L^{i}$ D. $\tiny \dpi{120} L^{+}=\bigcup_{i=1}^{.}L^{i}$ Option: B Explanation :
55:

If e1 and e2 are the regular expressions denoting the languages L1 and L2 respectively, then which of the following is wrong ?

 A. (e1) | (e2) is a regular expression denoting L1 ∪  L2 B. (e1) .(e2) is a regular expression denoting L1​. L2 C. φ is not a regular expression D. {ex} is a regular expression denoting L1* Option: C Explanation :