defpred S₁[ Point of (TOP-REAL 2)] means ( a <= $1 `1 & $1 `1 <= b & c <= $1 `2 & $1 `2 <= d );
{ p where p is Point of (TOP-REAL 2) : S₁[p] } c= the carrier of (TOP-REAL 2) from FRAENKEL:sch 10();
hence { p where p is Point of (TOP-REAL 2) : ( a <= p `1 & p `1 <= b & c <= p `2 & p `2 <= d ) } is Subset of (TOP-REAL 2) ; :: thesis: verum