k7*x7 - k1*x1 + k10*k13*x8 
k1*x1 + k9*x8 - k2*k13*x2 
k2*k13*x2 - k3*x3 
k3*x3 - k4*x4 
k4*x4 - k5*k13*x5 
k5*k13*x5 - k6*x6 
k6*x6 - k7*x7 - k8*x7 
k8*x7 - k9*x8 - k10*k13*x8 
x1 - k19 + x2 + x3 + x4 + x5 + x6 + x7 + x8 
