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