1
GATE CSE 2006
MCQ (Single Correct Answer)
+2
-0.6
If $$s$$ is a string over $${\left( {0 + 1} \right)^ * }$$ then let $${n_0}\left( s \right)$$ denote the number of $$0'$$ s in $$s$$ and $${n_1}\left( s \right)$$ the number of $$1'$$s in $$s.$$ Which one of the following languages is not regular?
A
$$L = \left\{ {s \in {{\left( {0 + 1} \right)}^ * }\left| {{n_0}\left( s \right)\,\,} \right.} \right.$$ is a $$3$$-digit prime$$\left. \, \right\}$$
B
$$L = \left\{ {s \in {{\left( {0 + 1} \right)}^ * }\left| {\,\,} \right.} \right.$$ for every prefix $$s'$$ of $$s.$$ $$\,\left| {{n_0}\left( {{s^,}} \right) - {n_1}\left( {{s^,}} \right)\left| { \le \left. 2 \right\}} \right.} \right.$$
C
$$L = \left\{ {s \in {{\left( {0 + 1} \right)}^*}\left\| {{n_0}\left( s \right) - {n_1}\left( s \right)\left| { \le \left. 4 \right\}} \right.} \right.} \right.$$
D
$$L = \left\{ {s \in {{\left( {0 + 1} \right)}^ * }} \right.\left| {{n_0}\left( s \right)} \right.$$ mod $$7 = {n_1}\left( s \right)$$ mod $$5 = \left. 0 \right\}$$
2
GATE CSE 2006
MCQ (Single Correct Answer)
+2
-0.6
Let $${L_1}$$ be a regular language, $${L_2}$$ be a deterministic context-free language and $${L_3}$$ a recursively enumerable, but not recursive, language. Which one of the following statement is false?
A
$${L_1} \cap {L_2}$$ is deterministic $$CFL$$
B
$${L_3} \cap {L_1}$$ is recursive
C
$${L_1} \cup {L_2}$$ is context-free
D
$${L_1} \cap {L_2} \cap {L_3}$$ is recursively enumerable
3
GATE CSE 2006
MCQ (Single Correct Answer)
+2
-0.6
For $$s \in {\left( {0 + 1} \right)^ * },$$ let $$d(s)$$ denote the decimal value of $$s(e. g.d(101)=5)$$
Let $$L = \left\{ {s \in {{\left( {0 + 1} \right)}^ * }\left| {\,d\left( s \right)\,} \right.} \right.$$ mod $$5=2$$ and $$d(s)$$ mod $$\left. {7 \ne 4} \right\}$$

Which of the following statement is true?

A
$$L$$ is recursively enumerable, but not recursive
B
$$L$$ is recursive, but not context-free
C
$$L$$ is context-free, but not regular
D
$$L$$ is regular
4
GATE CSE 2006
MCQ (Single Correct Answer)
+2
-0.6
Consider the following statements about the context-free grammar
$$G = \left\{ {S \to SS,\,S \to ab,\,S \to ba,\,S \to \varepsilon } \right\}$$
$$1.$$ $$G$$ is ambiguous
$$2.$$ $$G$$ produces all strings with equal number of $$a's$$ and $$b's$$
$$3.$$ $$G$$ can be accepted by a deterministic $$PDA$$.

Which combination below expresses all the true statements about $$G?$$

A
$$1$$ only
B
$$1$$ and $$3$$ only
C
$$2$$ and $$3$$ only
D
$$1, 2$$ and $$3$$
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