google "DTIME and time hierarchy theorem mathematics" and pick first outcome

]]>but the answer is still the same.

AB U BA could be decidable for some undecidable A, B.

]]>Let A contain all even-length strings, plus an undecidable collection of odd-length strings. Let B contain all odd-length strings, plus the empty string, plus an undecidable collection of even-length strings. So each is undecidable, but the concatenation AB consists of all strings and hence is decidable

]]>what was the solution for that?

]]>Time hierarchy theorem in wikipedia

it seems like the answer hides somewhere on that page

]]>search for "never moves three times to the left tm" in google and pick the first result

in the page search for "three". they give the answer (no solution) there.

for the configuration repetition search for

"repeats a configuration more than once turing"

pick the first result and see question 4.

because you can build a TM that in order to move left once - moves two times to the left, and one time to the right -

therefor is exactly as powerful as a regular TM, and therefor isn't in R.

AUB / AB U BA:

AUB could be decidable - if A = EMPTYtm. B= EMPTYtm^C (==MASHLIM), A and B are not decidable. but AUB is all encodings of TMs.

I can only guess that AB U BA is not decidable.

The questions of getting a language of TM M where M never moves left three times in a row. Was the answer R?

The question where M never repetes a configuration, what was the answer?

The question where we had to choose which could not be in R AUB / AB U BA, what was the answer?

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