formula

$\pi_[z] = \frac{0.493 \alpha_{[x]} \alpha_{[y]}- 0.413 \alpha_{[y]}- 0.413 \alpha_{[x]}+ 0.346}{1.75 \alpha_{[x]} \alpha_{[y]} \alpha_{[]} -1.11 (\alpha_{[x]} \alpha_{[y]}+\alpha_{[y]}c+c\alpha_{[x]}) + 0.544 (\alpha_{[x]}+\alpha_{[y]}+c) - 0.132}$