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Consider the following sentence:
"Prof. Godel cannot prove this sentence."
Is this sentence true? If it is true, can Prof. Godel prove it? If he can't, does it tell us anything about Prof. Godel? More generally, does it tell as anything about creative human mathematicians (who are supposed to be more than formal machines)?
A further (obvious) twist is the sentence:
"Nobody can prove this sentence."
Is this sentence true? If it is, how do you know?
The questions are, of course, philosophical, but Godel himself was thinking a lot about philosophical consequences of his theorems, so we can too.
"Prof. Godel cannot prove this sentence."
Is this sentence true? If it is true, can Prof. Godel prove it? If he can't, does it tell us anything about Prof. Godel? More generally, does it tell as anything about creative human mathematicians (who are supposed to be more than formal machines)?
A further (obvious) twist is the sentence:
"Nobody can prove this sentence."
Is this sentence true? If it is, how do you know?
The questions are, of course, philosophical, but Godel himself was thinking a lot about philosophical consequences of his theorems, so we can too.