'''Originally Posted By: peterle''' Use the Recursion Theorem to show HALTTM in undecidable<br><br>Proof by contradiction<br>Suppose H is a machine that decides HALTTM<br>H = { | M is a TM and M halts on w}<br>Consider the machine B = &quot;on input w:<br> *Obtain, via recursion theorem, own description *Run H on *accept if H rejects, reject if H accepts&quot; B accepts w iff H rejects <br>H rejects iff B rejects w<br>Contradiction - HALTTM is undecidable<br><br>Peter Le<br>Nicolas Seto<br>Jianqi Wang<br>Wenlong Zhang