0 votes 0 votes closed as a duplicate of: L= {<TM> | TM halts on every input} L = { <M> / M is a Turing machine and M accepts a regular language }. This Language L is recursively enumerable but not recursive. ...right ?? Theory of Computation theory-of-computation decidability recursive-and-recursively-enumerable-languages + – vignesh asked Apr 21, 2017 retagged Jul 4, 2017 by Arjun vignesh 311 views comment Share Follow See all 2 Comments See all 2 2 Comments reply Arpit Dhuriya commented May 15, 2017 reply Follow Share I think it reduces to ATM, so Recursively Enumerable. 0 votes 0 votes Rupendra Choudhary commented May 22, 2017 reply Follow Share Although i am unable to prove but as per my knowledge Regularity for TM is Undecidable . L={⟨M⟩∣M is a TM, LM∈REG} is undecidable not even semi-decidable. 1 votes 1 votes Please log in or register to add a comment.