{ diff(x1, t) = 0,
  diff(x2, t) = (1*k1*k2/(1 + (x3/k3)^k4) + (-1)*k1*k8*x2)/k1,
  diff(x3, t) = (1*k1*k5*delay(x2, k7)^k6 + (-1)*k1*k9*x3)/k1 }