reserve L for satisfying_Sh_1 non empty ShefferStr;

theorem Th54:
  for x, y, z being Element of L holds x | ((y | (y | (z | x))) |
  x) = y | ((x | (y | (x | z))) | y)
proof
  let x, y, z be Element of L;
  set Z = y | (x | z);
  (x | Z) | y = y | (z | x) by Th30;
  hence thesis by Th53;
end;
