1
GATE CSE 2022
MCQ (More than One Correct Answer)
+1
-0.33

Which of the following statements is/are TRUE?

A
Every subset of a recursively enumerable language is recursive.
B
If a language L and its complement $$\overline L$$ are both recursively enumerable, then L must be recursive.
C
Complement of a context-free language must be recursive.
D
If L1 and L2 are regular, then L1 $$\cap$$ L2 must be deterministic context-free.
2
GATE CSE 2022
MCQ (More than One Correct Answer)
+1
-0.33

Which of the following is/are undecidable?

A
Given two Turing machines M1 and M2, decide if L(M1) = L(M2).
B
Given a Turing machine M, decide if L(M) is regular.
C
Given a Turing machine M, decide if M accepts all strings.
D
Given a Turing machine M, decide if M takes more than 1073 steps on every string.
3
GATE CSE 2016 Set 2
+1
-0.3
Consider the following types of languages: $${L_1}:$$ Regular, $${L_2}:$$ Context-free, $${L_3}:$$ Recursive, $${L_4}:$$ Recursively enumerable. Which of the following is/are TRUE?

$$\,\,\,\,\,\,\,{\rm I}.\,\,\,\,\,\,\,$$ $$\overline {{L_3}} \cup {L_4}$$ is recursively enumerable
$$\,\,\,\,\,{\rm I}{\rm I}.\,\,\,\,\,\,\,$$ $$\overline {{L_2}} \cup {L_3}$$ is recursive
$$\,\,\,{\rm I}{\rm I}{\rm I}.\,\,\,\,\,\,\,$$ $$L_1^ * \cap {L_2}$$ is context-free
$$\,\,\,{\rm I}V.\,\,\,\,\,\,\,$$ $${L_1} \cup \overline {{L_2}}$$ is context-free

A
$${\rm I}$$ only
B
$${\rm I}$$ and $${\rm III}$$ only
C
$${\rm I}$$ and $${\rm IV}$$ only
D
$${\rm I},$$ $${\rm II}$$ and $${\rm III}$$ only
4
GATE CSE 2015 Set 2
+1
-0.3
Consider the following statements.

$$\,\,\,$$ $${\rm I}.\,\,\,\,\,\,\,\,\,$$ The complement of every Turing decidable language is Turing decidable
$$\,$$ $${\rm II}.\,\,\,\,\,\,\,\,\,$$ There exists some language which is in $$NP$$ but is not Turing decidable
$${\rm III}.\,\,\,\,\,\,\,\,\,$$ If $$L$$ is a language in $$NP,$$ $$L$$ is Turing decidable

Which of the above statements is/are true?

A
Only $${\rm I}$$$${\rm I}$$
B
Only $${\rm III}$$
C
Only $${\rm I}$$ and $${\rm II}$$
D
Only $${\rm I}$$ and $${\rm III}$$
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