decidability construct turing machine?

Let L be a decidable language. Show that the language L′ is also decidable, where

L′ = {w | w · w^r ∈ L},

and w · w^r is the concatenation of the word w with its inverse.

Can anyone help me with this?

(2 votes)
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KarlRanseierIII
1 year ago

What if you inverted the TM itself and 'merged' it with the original one?

Thus, the final state of the original TM is also the starting state of the inverted TM. The original starting state is then accepted by the inverted TM. The transitions are reversed, as is the tape direction.

Consider whether such a construction is feasible.

(This is just a spontaneous idea, maybe there is another way)

PS: The tape direction should not be inverted, of course, I shot too quickly….