3 ms·

Edit: Ah... I see now. By that logic, how is either (7,7) or (8,8) allowed?

• sidlls 4y ago
  "x:=(y|2); y:=(7|8); (x|y)" translates (roughly) to: (x|y) is a cartesian product--the set of all ordered pairs (X,Y) such that X is in x and Y is in Y, in order. x has 2 elements: X=y and X=2. y has 2 elements: Y=7 and Y=8. So the set of all ordered pairs is (X=Y, Y=7), (X=Y, Y=8), (X=2, Y=7), (X=2,Y=8). Since X=Y in the first two pairs, replace it with the value of Y from that pair: (X=7,Y=7), (X=8,Y=8).