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by ghkbrew 1019 days ago
Imagine you have an code which does #2. Now give it itself as an argument. What is the result? If it emits 0 then it's behaving according to #1, then because we assumed it satisfies #2 it must emit 1, a contradiction. Similarly it can't emit 1.

Thus it is impossible to have an algorithm which solves #2 for all inputs, because it must fail on at least one input (itself)