0 0 z a
0 0 z+1/3 a
0 0 z+2/3 a
1/2 1/2 z b
1/2 0 z+1/3 b
0 1/2 z+2/3 b
x y z c
-y x-y z+1/3 c
-x+y -x z+2/3 c
-x -y z c
y -x+y z+1/3 c
x-y x z+2/3 c