0 votes 0 votes $D = \left \{ <M> \mid \ M \text{ is a TM that rejects the input string } x \right \}$ What is complement of D and is it Decidable, Turing recognizable or not Turing recognizable? Theory of Computation decidability + – Mk Utkarsh asked Sep 15, 2018 • edited Sep 16, 2018 by Mk Utkarsh Mk Utkarsh 513 views answer comment Share Follow See all 10 Comments See all 10 10 Comments reply Show 7 previous comments Mk Utkarsh commented Sep 16, 2018 reply Follow Share so sir when we reduce halting problem to some other problem D, D only becomes undecidable(it maybe or may not be semi-decidable). according to you D is semi-decidable? 0 votes 0 votes Arjun commented Sep 16, 2018 reply Follow Share yes, exactly. But $D$ here is semi-decidable as for strings in $L$ there is no chance of infinite looping for TM. 1 votes 1 votes Mk Utkarsh commented Sep 16, 2018 reply Follow Share Arjun thanks sir i think i have cleared most of my doubts. 1 votes 1 votes Please log in or register to add a comment.