0 0 z a
1/2 1/2 z+1/2 a
0 1/2 z b
0 1/2 z+1/2 b
1/2 0 z+1/2 b
1/2 0 z b
x x z c
-x -x z c
-x+1/2 x+1/2 z+1/2 c
x+1/2 -x+1/2 z+1/2 c
x y z d
-x -y z d
-y+1/2 x+1/2 z+1/2 d
y+1/2 -x+1/2 z+1/2 d
x+1/2 -y+1/2 z+1/2 d
-x+1/2 y+1/2 z+1/2 d
-y -x z d
y x z d