• affiliate@lemmy.worldOP
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      11 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

        • affiliate@lemmy.worldOP
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          11 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
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            11 months ago

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

            • affiliate@lemmy.worldOP
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              11 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.

          • Lem Jukes@lemm.ee
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            11 months ago

            Give it up for op actually out here answering questions like a real live teacher.