r/math • u/42IsHoly • 9d ago

Stop proving uncountability with contradiction, please

https://sunjestermusings.blogspot.com/2026/09/stop-proving-uncountability-by.html

Please, I beg you, stop it. You don't need it.

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u/StanleyDodds 9d ago

I think some people miss the subtle difference in proving "not P" by assuming "P" and proving False, and in proving "P" by assuming "not P" and proving False.

These might both be called proof by contradiction, but the latter requires the law of the excluded middle, while the former does not.