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