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I know ¬H is not semidecidable so I was thinking of creating a language that combines both H and ¬H. Therefore L would be undecidable for ¬H and ¬L would be undecidable for H. Is this a proper approach for this question or am I completely off mark?
I also have few other questions, give an example of a language where: 1) L ∈ D and ¬L ∈ SD − D? 2) L, ¬L ∈ SD − D?
For 1) I know D is closed under complement therefore ¬L must be decidable iff L is decidable. So there are no examples?
For 2) I know if both L and ¬L are SD, then L must be decidable. So there are also no examples?
Sorry for some these questions, I am 90% sure I am right but I'm learning everything by myself so I have no one to ask to be sure. Thanks for any help.