Decidability

Question

Answer 1

I think first 2 are undeciable problems because if you can one can build TM to find out all TM's which halt on every input and which halts on no input ,even halting problem can be decided by using this program as subprogram(reducibality).3rd one is recognizable/recursive enumarable but not decidable as well.4th one I have some doubt.

Comments

I think 1 is Recursive bcoz in Recursive, TM halts by either accepting or rejecting. 2 is Non-R.  3 and 4 are RE but not REC

Answer 2

https://gateoverflow.in/93284/l-tm-tm-halts-on-every-input?show=93284#q93284

Comments

All are undecidable and all are recursive enumerable

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1) Not RE, using rice theorem

2)not RE

3) RE but not recursive.

4)not RE.