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addition rule (lemmy.world)

submitted 6 months ago by [email protected] to c/[email protected]

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[–] [email protected] 27 points 6 months ago (2 children)

× 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

[–] [email protected] 12 points 6 months ago (1 children)

What does type() mean here?

[–] [email protected] 24 points 6 months ago (2 children)

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)

[–] [email protected] 10 points 6 months ago (1 children)

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

[–] [email protected] 15 points 6 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.

[–] [email protected] 8 points 6 months ago

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

[–] [email protected] 2 points 6 months ago

Oh wow, I should know that... Thanks