# 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:

- 5
*x*+ 3*y*< 2 - (
*x*< -2) ∧ (*x*+*y*= 4) *TallerThan =*{(*name*_{1 },*name*_{2}) ∈*Students*^{ 2 }|*name*_{1 }is taller than*name*_{2}}*NearbyCities*= {(*city*_{1},*city*_{2 }) ∈*USCities*^{ 2 }|*dist*(*city*_{1},*city*_{2 }) ≤ 50}