Contoh himpunan A={x∈ℝ:2≤x≤5}, B={x∈ℝ:3≤x≤7}, 
C={y∈ℝ:1≤y≤3}, D={y∈ℝ:2≤y≤4}, membuktikan (A∩B)×(C∩D) = (A×C)∩(B×D) .