• affiliate@lemmy.worldOP
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      1 year 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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          1 year 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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            1 year ago

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

            • affiliate@lemmy.worldOP
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              1 year 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.