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