reserve L for satisfying_Sh_1 non empty ShefferStr;

theorem Th34:
  for x, y, z being Element of L holds x | (y | (x | (z | (y | x)) )) = x | x
proof
  let x, y, z be Element of L;
  (x | (y | (x | (z | (y | x))))) | (x | (z | (y | x))) = x by Th31;
  hence thesis by Th18;
end;
