{ diff(x1, t) = ((-1)*k1*k4*x1/k2/((1 + x1/k2)*(1 + x8/k3)) + 1*k1*k18*x9*x2/k17/(1 + x2/k17))/k1,
  diff(x2, t) = (1*k1*k4*x1/k2/((1 + x1/k2)*(1 + x8/k3)) + (-1)*k1*k18*x9*x2/k17/(1 + x2/k17))/k1,
  diff(x3, t) = ((-1)*k1*k8*x2*x3/k6/(1 + x3/k6 + x4/k6)*(1 + k5*x8/k7)/(1 + x8/k7) + 1*k1*k22*x10*x4/k21/(1 + x5/k21 + x4/k21))/k1,
  diff(x4, t) = (1*k1*k8*x2*x3/k6/(1 + x3/k6 + x4/k6)*(1 + k5*x8/k7)/(1 + x8/k7) + (-1)*k1*k12*x2*x4/k10/(1 + x4/k10 + x3/k10)*(1 + k9*x8/k11)/(1 + x8/k11) + 1*k1*k20*x10*x5/k19/(1 + x5/k19 + x4/k19) + (-1)*k1*k22*x10*x4/k21/(1 + x5/k21 + x4/k21))/k1,
  diff(x5, t) = (1*k1*k12*x2*x4/k10/(1 + x4/k10 + x3/k10)*(1 + k9*x8/k11)/(1 + x8/k11) + (-1)*k1*k20*x10*x5/k19/(1 + x5/k19 + x4/k19))/k1,
  diff(x6, t) = ((-1)*k1*k14*x5*x6/k13/(1 + x6/k13 + x7/k13) + 1*k1*k26*x11*x7/k25/(1 + x8/k25 + x7/k25))/k1,
  diff(x7, t) = (1*k1*k14*x5*x6/k13/(1 + x6/k13 + x7/k13) + (-1)*k1*k16*x5*x7/k15/(1 + x6/k15 + x7/k15) + 1*k1*k24*x11*x8/k23/(1 + x8/k23 + x7/k23) + (-1)*k1*k26*x11*x7/k25/(1 + x8/k25 + x7/k25))/k1,
  diff(x8, t) = (1*k1*k16*x5*x7/k15/(1 + x6/k15 + x7/k15) + (-1)*k1*k24*x11*x8/k23/(1 + x8/k23 + x7/k23))/k1,
  diff(x9, t) = 0/k1,
  diff(x10, t) = 0/k1,
  diff(x11, t) = 0/k1 }