{ diff(x1, t) = (1*k17*k16 + (-1)*k17*k15*x1 + (-1)*k17*x1*k7*k20*k21/(1 + k21)/(k4 + k20 + x10))/k17,
  diff(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,
  diff(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,
  diff(x5, t) = 0,
  diff(x7, t) = 0,
  diff(x8, t) = 0,
  diff(x11, t) = 0 }