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