theorem Th35:
  p <= 0 iff numerator(p) <= 0
proof
  now
    assume
A1: numerator(p)<=0;
    per cases by A1;
    suppose
      numerator(p)=0;
      hence p<=0 by Th11;
    end;
    suppose
      numerator(p)<0;
      hence p<=0;
    end;
  end;
  hence thesis;
end;
