Typo in the first proof of Cantor's theorem (you got in vs not in mixed up in the second case).

I hadn't noticed before that Cantor's theorem and Russell's paradox were exactly the same argument. This makes me curious as to how Cantor failed to notice Russell's paradox.

Edit: It appears that Cantor actually did figure out that Cantor's theorem leads to things like Russell's paradox in 1899, two years before Russell did.