• @affiliateOP
      link
      2810 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

        • @affiliateOP
          link
          2510 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)

            • @affiliateOP
              link
              1510 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
            link
            fedilink
            810 months ago

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

    • Jack Riddle
      link
      fedilink
      510 months ago

      × is the cartesian product I think, no clue what the other thing is tho