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I am currently struggling with figuring out the following problem:

Given decidable languages L1, L2, L3, L4, ...

Is the infinite union of Languages L1, ...... decidable? I have an intution that it is not, but I cannot find an example against that thesis.

Thank you in advance

Druckermann
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1 Answers1

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Your intuition is right.

Hint: for any $x$, the language $\{x\}$ is decidable. Think how we can use this fact to construct an undecidable language.

nir shahar
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