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Previous Year Question (PYQs)
1
Given below are two statements:
Statement I: The problem "Is $L_1\cap L_2=\phi$?" is undecidable for context sensitive languages $L_1$ and $L_2$.
Statement II: The problem "Is $W\in L$?" is decidable for context sensitive language $L$, where $W$ is a string.
In the light of the above statements, choose the correct answer from the options given below:
Solution
Statement I is true.
For context sensitive languages, the emptiness problem is undecidable.
Since context sensitive languages are closed under intersection, checking whether:
$L_1\cap L_2=\phi$
is also undecidable.
So, Statement I is true.
Statement II is also true.
Membership problem for context sensitive languages is decidable.
This is because context sensitive languages are accepted by Linear Bounded Automata, and for a fixed input there are only finitely many configurations.
Therefore, we can decide whether $W\in L$ or not.
So, both statements are true.
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