[ Eq(Derivative(x1, t), (1*k1*k2*k13 + (-1)*k1*x1*k13 + (-1)*k3*x2*x1*k13 + 1*k4*x3*k13 + 1*k6*x4*k13)/k12),
  Eq(Derivative(x2, t), ((-1)*k3*x2*x1*k13 + 1*k4*x3*k13 + 1*k6*x4*k13)/k11),
  Eq(Derivative(x3, t), (1*k3*x2*x1*k13 + (-1)*k4*x3*k13 + (-1)*k5*x3*k13)/k12),
  Eq(Derivative(x4, t), (1*k5*x3*k13 + (-1)*k6*x4*k13 + (-1)*k7*x4*k13 + (-1)*k8*x4*k13)/k13),
  Eq(Derivative(x5, t), 1*k7*x4*k13/k13),
  Eq(Derivative(x6, t), 1*k8*x4*k13/k11) ]