If X and Y are two sets, then X × Y is the Cartesian product of X and Y, which is the set of all pairs (x, y) such that x ∈ X and y ∈ Y.
This means
A × A = {(1, 1), (1, 2), (1, 3), (2, 1), (2, 2), (2, 3), (3, 1), (3, 2), (3, 3)}
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