GATE CSE 2022 Q23: True statements about RE, recursive, CFL and regular languages

Which of the following statements is/are TRUE?

Try it: multiple select: one or more correct options

Select all correct options. No negative marking, no partial marks.

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Answer: B, C, D (official GATE 2022 final answer key)

Concept used: Closure properties: recursive languages are closed under complement, and regular languages under intersection.

First step: For (A), note $\Sigma^*$ is recursively enumerable and contains every language, including undecidable ones.

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Source: official GATE 2022 CS question paper and final answer key, organised by IIT Kharagpur. Question paper · Answer key