theorem Th4:
  [r,s] in RealOrd implies r <= s
proof
  hereby
    assume [r,s] in RealOrd;
    then consider r1,s1 being Real such that
A1: [r,s] = [r1,s1] and
A2: r1 <= s1;
    r = r1 by A1,XTUPLE_0:1;
    hence r <= s by A1,A2,XTUPLE_0:1;
  end;
end;
