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Cantor's diagonal argument. I learned it all in high-school!
by memming 13y ago
Cantor's diagonal argument. I learned it all in high-school!
- ColinWright 13y agoYou learned it, but the author worked it out for himself. Good for him - kudos.
- xerula 13y agoHe had probably previously encountered Cantor's diagonalization technique for proving the uncountability of the reals. He just saw how to apply the same technique to the question of describability.
- vbuterin 13y agoIt's important to note that the "diagonal argument" used to show countability of rationals or describable numbers is completely different from the one used to show the uncountability of the reals. In fact, the two counting arguments used to show countability of rationals and describable numbers are themselves quite different (I would say the latter isn't even a diagonal argument at all; it just goes through a countable union of finite sets one by one).
- deleted 13y ago[deleted]