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

theorem Th37:
  for L being satisfying_DN_1 non empty ComplLLattStr, x, y, z
  being Element of L holds x + ((y + z)` + (y + x)`)` = y + x
proof
  let L be satisfying_DN_1 non empty ComplLLattStr;
  let x, y, z be Element of L;
  x + ((y + z)` + (y + x)`)` = (y + x )`` by Th26;
  hence thesis by Th23;
end;
