{ diff(x1, t) = (-(k1*x5 + k9*x7))*x1,
  diff(x2, t) = (-k2)*(1 + k10)*x4*x2,
  diff(x3, t) = (-k4)*x6*x3,
  diff(x4, t) = (k1*x5 + k9*x7)*x1 - k5*x4,
  diff(x5, t) = k2*x4*x2 - k3*x7*x5 - k6*x5,
  diff(x6, t) = k2*k10*x4*x2 + k3*x7*x5 - k7*x6,
  diff(x7, t) = k4*x6*x3 - k8*x7 }