-(а-c+d)+a-(c+d)-(d-c)-с = -a + c - d + a - c - d - d + c = - 3d
-а+с-d+a-c-d-d+c-c=(-a+a)+(c-c+c-c)+(-d-d-d)=-3d
-(а-c+d)+a-(c+d)-(d-c)-с = -a + c - d + a - c - d - d + c = - 3d
-а+с-d+a-c-d-d+c-c=(-a+a)+(c-c+c-c)+(-d-d-d)=-3d