In the "Halting Problem" lecture, the prof. introduced a magic trick to use the fact that there exists no TM that accepts all other TM that accept themselves to prove that the halting problem is undecidable. There he asked to change the algorithm to alternate the answer i.e if the answer is yes change it to no and vice versa. Then he proved that the halting problem is undecidable. I kind of didn't get his magic trick for the proof. It would be great if somebody can shed some light on it. Thanks!
https://www.youtube.com/watch?v=e9zzY7uqT8g
