[ Eq(Derivative(x1, t), ((-1)*k6*k4*x1*x5 + 1*k6*k1 + (-1)*k6*k5*x1)/k6),
  Eq(Derivative(x2, t), ((-1)*k6*k4*x2*x5 + 1*k6*k2 + (-1)*k6*k5*x2)/k6),
  Eq(Derivative(x3, t), (1*k6*k4*x1*x5 + (-1)*k6*k3*x3)/k6),
  Eq(Derivative(x4, t), (1*k6*k4*x2*x5 + (-1)*k6*k3*x4)/k6),
  Eq(Derivative(x5, t), ((-1)*k6*k4*x1*x5 + (-1)*k6*k4*x2*x5 + 1*k6*k3*x3 + 1*k6*k3*x4)/k6),
  Eq(Derivative(x6, t), 0/k6) ]