c_1, x_1, x_2, x_4, x_5, x_6, x_7, x_8, x_9, 
x_6
x_9
2*x_1+x_4
2*x_1*x_7^2+x_2
c_1*x_1+3*x_1*x_5+3*c_1
-2*c_1*x_2*x_7+x_1*x_7+x_1*x_8
