x x 0 a
-x -x 1/2 a
-x+1/2 x+1/2 1/4 a
x+1/2 -x+1/2 3/4 a
x y z b
-x -y z+1/2 b
-y+1/2 x+1/2 z+1/4 b
y+1/2 -x+1/2 z+3/4 b
-x+1/2 y+1/2 -z+1/4 b
x+1/2 -y+1/2 -z+3/4 b
y x -z b
-y -x -z+1/2 b