Which one of the following statements is equivalent to the following assertion? Turing machine M decides the language L ⊆ {0,1}*
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GATE CSE 2026 Set 2 · Q13
Time
Select one answerSingle correct
Solution
Official answer: D) Turing machine M accepts all input strings in L and rejects all input strings in {0,1}* - L
Turing Machines and UndecidabilityBy definition, a Turing machine is said to decide a language (where ) if:
halts and accepts every string .
halts and rejects every string (i.e., every string ).
Thus, accepts all strings in and rejects all strings in .
Hence, option (D) is the correct statement.
Try the question first, then check your work.
Examiner trap
Recall the definition of a language decider: it must halt on all inputs, accepting strings in the language and explicitly rejecting strings not in the language.
This Turing Machines and Undecidability previous year question is Q13 of the GATE CSE 2026 Set 2 paper. Find more GATE CSE PYQs on Turing Machines and Undecidability in Theory of Computation, or browse all GATE CSE PYQs.
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Turing Machines and Undecidability has 30 GATE CSE PYQs across 20 papers from 2012 to 2026. 13 of them are 1-mark MCQs like this one, and it is the only one in GATE CSE 2026 Set 2.
How GATE tests Turing Machines and UndecidabilityIndependent practice explanation verified by the GateAI team. GATE is conducted by the IITs; question text follows the official paper.