Links 2/19/11

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I'll continue my explanation of the ordinal numbers, starting with a nifty trick. Yesterday, I said that the collection of all ordinals is *not* a set, but rather a proper class. There's another really neat way to show that.
I've talked about the idea of the size of a set; and I've talked about the well-ordering theorem, that there's a well-ordering (or total ordering) definable for any set, including infinite ones.
With ordinals, we use exponents to create really big numbers. The idea is that we can define ever-larger families of transfinite ordinals using exponentiation. Exponentiation is defined in terms of repeated multiplication, but it allows us to represent numbers that we
In addition to the classic {L|R} version of the surreal numbers, you can also describe surreals using something called a sign expansion, where they're written as a sequence of "+"s and "-"s - a sort of binary representation of surreal numbers.