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submitted 9 months ago by affiliate@lemmy.world to c/196@lemmy.blahaj.zone

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[-] affiliate@lemmy.world 28 points 9 months ago

× is the cartesian product and = {x, {x,y}} is the ordered pair of x and y. (i.e., if x is in X and y is in Y, then is the corresponding element of the cartesian product X × Y). hope this helps

[-] rasensprenger@feddit.de 12 points 9 months ago

What does type() mean here?

[-] affiliate@lemmy.world 25 points 9 months ago

it's the "order type" of a well ordering on a set. so, given a set X with a total ordering R, type(X,R) is the unique ordinal isomorphic to (X,R)

[-] bort@feddit.de 11 points 9 months ago

what's with the square at the end? isn't that usually for proofs?

[-] affiliate@lemmy.world 15 points 9 months ago

yeah but sometimes when the textbook authors are feeling particularly mischievous they'll just put them in random places. and sometimes they'll even skip the proofs but keep the square.