{ diff(x1, t) = ((-1)*k2*k6*x1/k4/(1 + x1/k4)*(1 + k3*x8/k5)/(1 + x8/k5) + 1*k2*k18*x9*x2/k17/(1 + x2/k17))/k2,
  diff(x2, t) = (1*k2*k6*x1/k4/(1 + x1/k4)*(1 + k3*x8/k5)/(1 + x8/k5) + (-1)*k2*k18*x9*x2/k17/(1 + x2/k17))/k2,
  diff(x3, t) = ((-1)*k2*k9*x2*x3/k7/((1 + x3/k7 + x4/k7)*(1 + x8/k8)) + 1*k2*k22*x10*x4/k21/(1 + x5/k21 + x4/k21))/k2,
  diff(x4, t) = (1*k2*k9*x2*x3/k7/((1 + x3/k7 + x4/k7)*(1 + x8/k8)) + (-1)*k2*k12*x2*x4/k10/((1 + x3/k10 + x4/k10)*(1 + x8/k11)) + 1*k2*k20*x10*x5/k19/(1 + x5/k19 + x4/k19) + (-1)*k2*k22*x10*x4/k21/(1 + x5/k21 + x4/k21))/k2,
  diff(x5, t) = (1*k2*k12*x2*x4/k10/((1 + x3/k10 + x4/k10)*(1 + x8/k11)) + (-1)*k2*k20*x10*x5/k19/(1 + x5/k19 + x4/k19))/k2,
  diff(x6, t) = ((-1)*k2*k14*x5*x6/k13/(1 + x6/k13 + x7/k13) + 1*k2*k26*x11*x7/k25/(1 + x8/k25 + x7/k25) + (-1)*k2*(k39*x6 - k40*x17))/k2,
  diff(x7, t) = (1*k2*k14*x5*x6/k13/(1 + x6/k13 + x7/k13) + (-1)*k2*k16*x5*x7/k15/(1 + x6/k15 + x7/k15) + 1*k2*k24*x11*x8/k23/(1 + x8/k23 + x7/k23) + (-1)*k2*k26*x11*x7/k25/(1 + x8/k25 + x7/k25) + (-1)*k2*(k41*x7 - k42*x18))/k2,
  diff(x8, t) = (1*k2*k16*x5*x7/k15/(1 + x6/k15 + x7/k15) + (-1)*k2*k24*x11*x8/k23/(1 + x8/k23 + x7/k23) + (-1)*k2*(k27*x8 - k28*x12))/k2,
  diff(x9, t) = 0/k2,
  diff(x10, t) = 0/k2,
  diff(x11, t) = 0/k2,
  diff(x12, t) = (1*k2*(k27*x8 - k28*x12) + (-1)*k2*k43*x16*x12/k44/(1 + x12/k44 + x18/k45))/k2,
  diff(x13, t) = (1*k2*k29*x12^k30/(k31^k30 + x12^k30) + (-1)*k2*k32*x13)/k2,
  diff(x14, t) = (1*k2*k32*x13 + (-1)*k2*k33*x14)/k2,
  diff(x15, t) = (1*k2*k34*x14 + (-1)*k2*(k35*x15 - k36*x16) + (-1)*k2*k37*x15)/k2,
  diff(x16, t) = (1*k2*(k35*x15 - k36*x16) + (-1)*k2*k38*x16)/k2,
  diff(x17, t) = (1*k2*(k39*x6 - k40*x17) + 1*k2*k46*x16*x18/k47/(1 + x18/k47 + x12/k48))/k2,
  diff(x18, t) = (1*k2*(k41*x7 - k42*x18) + 1*k2*k43*x16*x12/k44/(1 + x12/k44 + x18/k45) + (-1)*k2*k46*x16*x18/k47/(1 + x18/k47 + x12/k48))/k2 }