2025-03-01 14:26:36 +01:00

157 B

X \times Y = \{ x: \{ 1, 2 \} \to x_{1} \cup x_{2} | x_{1} X_{1} \wedge x_{2} \in X_{2} \}

where X = X_{1} and Y = X_{2}, basically (X_{1}, X_{2}).