2 z - 2*z + 1
z^2 - 2*z + 1
x - 1
2 1 + z - 2*z
1 + z^2 - 2*z
1.0 + z^2 - 2.0*z
2 (-1 + z)
(-1 + z)^2
1 + z*(-2 + z)