reserve L for satisfying_Sh_1 non empty ShefferStr;

theorem Th33:
  for x, y, z being Element of L holds x | (y | z) = x | (z | y)
proof
  let x, y, z be Element of L;
  (z | (x | (z | y))) | x = x | (z | y) by Th28;
  hence thesis by Th30;
end;
