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