Saturday

January 31, 2015

January 31, 2015

Posted by **Elizabeth** on Sunday, November 22, 2009 at 1:54pm.

How do I make sense of this?

"So suppose I have a black box which can decide the halting problem, that is I can give it a program P and the box tells me if P will ever stop.

Using this I can make a program P' that works as follows:

Given a program P ask the box if P will stop.

If P will halt run forever.

If P will run forever, halt.

Last step, give P' as input to itself, if P' will run forever it must halt. "

I don't understand why there is a P' here? And why we have regular P and P'. I'm so confused.

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