fun f((a,b),(c,d)) =
             if a<c then LESS
             else if a>c then GREATER
                 (* here a=c *)
             else if b<d then LESS
             else if b>d then GREATER
             else EQUAL;

     f((1,2),(3,4));

     f((1,3),(1,2));

     f((4,5),(4,5));