(x+y+z)^2—(-x+y+z)^2+(x-y+z)^2-(x+y-z)^2
=(x+y+z-x+y+z)(x+y+z+x-y-z) +(x-y+z+x+y-z)(x-y+z-x-y+z)
=4x(y+z)-4x(y-z)
=8xz