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Results tagged with undecidability
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user 149550
Questions about problems which cannot be solved by any Turing machine.
1
vote
1
answer
2k
views
Prove that Turing Machine ever writes a blank symbol over a non blank symbol is undecidable
I have been given the following problem from the book Introduction to the Theory of Computation by Michael Sipser and was wondering if my solution is correct: Determine if a Turing Machine ever writes …
- 201
4
votes
2
answers
1k
views
How to show that the NECESSARY_CFG is Turing-recognizable but undecidable?
I have been given the following problem and was wondering if my solution is correct: Say that a variable $A$ in CFG $G$ is necessary if it appears in every derivation of some string $w$ where $w$ is i …
- 201