reserve L for satisfying_DN_1 non empty ComplLLattStr;
reserve x, y, z for Element of L;

theorem Th41:
  for L being satisfying_DN_1 non empty ComplLLattStr, x, y, z
  being Element of L holds (((x + y`) + z)` + y)`` = y
proof
  let L be satisfying_DN_1 non empty ComplLLattStr;
  let x, y, z be Element of L;
  (((x + y`) + z)` + y)` + (y` + y)` = (((x + y`) + z)` + y)` by Th32;
  hence thesis by Th36;
end;
