reserve i for Integer,
  a, b, r, s for Real;

theorem Th32:
  a <= b & r <= s implies Trectangle(a,b,r,s) is non empty
proof
  assume a <= b & r <= s;
  then |[a,r]| in closed_inside_of_rectangle(a,b,r,s) by Th31;
  hence the carrier of Trectangle(a,b,r,s) is non empty;
end;
