theorem Th24: :: JORDAN1:30

for s1, s2, t1, t2 being Real holds { pq where pq is Point of (TOP-REAL 2) : ( not s1 <= pq `1 or not pq `1 <= s2 or not t1 <= pq `2 or not pq `2 <= t2 ) } is Subset of (TOP-REAL 2)