Predicates on product sets

If (x,y) is variable over X ´ Y, then x is variable over X and y is variable over Y. So a predicate over X ´ Y has the forms:

• 5x + 3y < 2
• (x < -2) Ù (x + y = 4)
• TallerThan = {(name₁ , name₂) Î Students ² | name₁ is taller than name₂ }
• NearbyCities = {(city₁ , city₂ ) Î USCities ² | dist(city₁ , city₂ ) £ 50}