
theorem Th5:
  for N being directed non empty RelStr, x,y being Element of N ex
  z being Element of N st x <= z & y <= z
proof
  let N be directed non empty RelStr, x,y be Element of N;
  [#]N is directed by WAYBEL_0:def 6;
  then ex z being Element of N st z in [#]N & x <= z & y <= z by WAYBEL_0:def 1
;
  hence thesis;
end;
