z = \omega^1/3 \cdot e^2\pi i k / 3 = e^2\pi i/9 \cdot e^2\pi i k / 3 = e^2\pi i (1/9 + k/3) = e^2\pi i (1/9 + 3k/9) = e^2\pi i (3k+1)/9, \quad k = 0,1,2 - Groen Casting