[ Eq(Derivative(x1, t), (1*k10*k1/(1 + x2**k3) + (-1)*k10*k11*x1)/k10),
  Eq(Derivative(x2, t), (1*k10*k2/(1 + (x1/(1 + x3/k8)**k9)**k4) + (-1)*k10*k12*x2)/k10),
  Eq(Derivative(x3, t), 0/k10) ]