[ Eq(Derivative(x1, t), (1*k17*k16 + (-1)*k17*k15*x1 + (-1)*k17*x1*k7*k20*k21/(1 + k21)/(k4 + k20 + x10))/k17),
  Eq(Derivative(x2, t), (1*k17*k16 + (-1)*k17*k15*x2 + (-1)*k17*x2*k7*k20*k21/(1 + k21)/(k4 + k20 + x10) + (-1)*k17*x2*k7*k8*k19*k21/(k1 + k21)/(k2/k3*(k3 + x3 + k6*(k18 - x3)) + k19 + x9))/k17),
  Eq(Derivative(x3, t), (1*k17*k18/k9 + (-1)*k17*1/k9*x3 + (-1)*k17*x3*k7*k8*k19*k21/(k1 + k21)/(k3/k2*(k2 + x9) + x3 + k6*(k18 - x3)))/k17),
  Eq(Derivative(x5, t), 0),
  Eq(Derivative(x7, t), 0),
  Eq(Derivative(x8, t), 0),
  Eq(Derivative(x11, t), 0) ]