theorem Th24:
  for s1,s2,t1,t2 holds { pq where pq is Point of TOP-REAL 2:
  not (s1<=pq`1 & pq`1<=s2 & t1<=pq`2 & pq`2<=t2)} is Subset of TOP-REAL 2
proof
  let s1,s2,t1,t2;
  { |[ sb,tb ]|:not (s1<=sb & sb<=s2 & t1<=tb & tb<=t2)}
  is Subset of TOP-REAL 2 by Lm2,Lm8;
  hence thesis by Th22;
end;
