x_1, x_2, x_3, x_4, x_5, x_6, x_7, x_8, 
x_2
-3*x_3*x_4+4*x_8
4*x_6^2+x_3
4*x_5*x_6-x_3
8*x_1*x_7^2+x_3*x_4
