1
GATE CSE 2016 Set 1
+1
-0.3
Which one of the following regular expressions represents the language: the set of all binary strings having two consecutive $$0s$$ and two consecutive $$1s?$$
A
$$\left( {0 + 1} \right){}^ * 0011\left( {0 + 1} \right){}^ * + \left( {0 + 1} \right){}^ * 1100\left( {0 + 1} \right){}^ *$$
B
$$\left( {0 + 1} \right){}^ * \left( {00\left( {0 + 1} \right){}^ * 11 + 11\left( {0 + 1} \right){}^ * \left. {00} \right)} \right.\left( {0 + 1} \right){}^ *$$
C
$$\left( {0 + 1} \right){}^ * 00\left( {0 + 1} \right){}^ * + \left( {0 + 1} \right){}^ * 11\left( {0 + 1} \right){}^ *$$
D
$$00\left( {0 + 1} \right){}^ * 11 + 11\left( {0 + 1} \right){}^ * 00$$
2
GATE CSE 2016 Set 1
+2
-0.6
Consider the transition diagram of a $$PDA$$ given below with input alphabet $$\sum {\, = \left\{ {a,b} \right\}}$$ and stack alphabet $$\Gamma = \left\{ {X,Z} \right\}.$$ $$Z$$ is the initial stack symbol. Let $$L$$ denote the language accepted by the $$PDA.$$

Which one of the following is TRUE?

A
$$L = \left\{ {{a^n}{b^n}|n \ge 0} \right\}$$ and is not accepted by any finite automata
B
$$L = \left\{ {{a^n}|n \ge 0} \right\} \cup \left\{ {{a^n}{b^n}|n \ge 0} \right\}$$ and is not accepted by any deterministic $$PDA$$
C
$$L$$ is not accepted by any Turing machine that halts on every input
D
$$L = \left\{ {{a^n}|n \ge 0} \right\} \cup \left\{ {{a^n}{b^n}|n \ge 0} \right\}$$ and is deterministic context-free
3
GATE CSE 2016 Set 1
+2
-0.6
Consider the following context-free grammars:
\eqalign{ & {G_1}:\,\,\,\,\,S \to aS|B,\,\,B \to b|bB \cr & {G_2}:\,\,\,\,\,S \to aA|bB,\,\,A \to aA|B|\varepsilon ,\,\,B \to bB|\varepsilon \cr}

Which one of the following pairs of languages is generated by $${G_1}$$ and $${G_2}$$, respectively?

A
$$\left\{ {{a^m}{b^n}|m > 0\,\,\,\,} \right.$$ or $$\,\,\,\,$$$$n > \left. 0 \right\}$$ and $$\left\{ {{a^m}{b^n}|m > 0\,\,\,\,} \right.$$ and $$\,\,\,\,n > \left. 0 \right\}\,\,\,\,$$
B
$$\left\{ {{a^m}{b^n}|m > 0\,\,\,\,} \right.$$ and $$\,\,\,n > \left. 0 \right\}\,\,\,\,$$ and $$\left\{ {{a^m}{b^n}|m > 0\,\,\,\,} \right.$$ or $$\,\,\,\,n \ge \left. 0 \right\}$$
C
$$\left\{ {{a^m}{b^n}|m \ge 0\,\,\,\,} \right.$$ or $$\,\,\,\,n > \left. 0 \right\}\,\,\,\,$$ and $$\left\{ {{a^m}{b^n}|m > 0\,\,\,\,} \right.\,$$ and $$\,\,\,\,n > \left. 0 \right\}\,\,\,\,$$
D
$$\left\{ {{a^m}{b^n}|m \ge 0\,\,\,\,} \right.$$ and $$\,\,\,n > \left. 0 \right\}\,\,\,\,$$ and $$\left\{ {{a^m}{b^n}|m > 0\,\,\,\,} \right.\,$$ or $$\,\,\,\,n > \left. 0 \right\}\,\,\,\,$$
4
GATE CSE 2016 Set 1
+2
-0.6
Let $$X$$ be a recursive language and $$Y$$ be a recursively enumerable but not recursive language. Let $$W$$ and $$Z$$ be two languages such that $$\overline Y$$ reduces to $$W,$$ and $$Z$$ reduces to $$\overline X$$ (reduction means the standard many-one reduction). Which one of the following statements is TRUE?
A
$$W$$ can be recursively enumerable and $$Z$$ is recursive.
B
$$W$$ can be recursive and $$Z$$ is recursively enumerable.
C
$$W$$ is not recursively enumerable and $$Z$$ is recursive.
D
$$W$$ is not recursively enumerable and $$Z$$ is not recursive.
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