{ diff(x1, t) = ((-1)*k27*x1 + 1*k25*x7 + 1*k14*x2)/k32,
  diff(x2, t) = ((-1)*k7*x2 + 1*k26*x8 + (-1)*k14*x2)/k32,
  diff(x3, t) = (1*k16*x10 + 1*k14*x6 + (-1)*k28*x3)/k32,
  diff(x4, t) = ((-1)*k5*x4 + (-1)*k14*x4 + 1*k11*x11)/k32,
  diff(x5, t) = ((-1)*k10*x5 + 1*k14*x4 + 1*k29*x9)/k32,
  diff(x6, t) = ((-1)*k6*x6 + (-1)*k14*x6 + 1*k12*x12)/k32,
  diff(x7, t) = (1*k27*x1 + (-1)*k30/k3*x7/(1 + x7/k3 + x7/k4 + x8/k1 + x8/k2) + (-1)*k18/k4*x7/(1 + x7/k3 + x7/k4 + x8/k1 + x8/k2) + (-1)*k21*x7/(k22 + x7 + x7*x7/k23) + 1*(k13 + k24)*x8 + (-1)*k25*x7 + (-1)*k17*((1 - k9)/k9*x7 - x17))/k33,
  diff(x8, t) = (1*k7*x2 + (-1)*k19/k1*x8/(1 + x7/k3 + x7/k4 + x8/k1 + x8/k2) + (-1)*k20/k2*x8/(1 + x7/k3 + x7/k4 + x8/k1 + x8/k2) + 1*k21*x7/(k22 + x7 + x7*x7/k23) + (-1)*(k13 + k24)*x8 + (-1)*k26*x8 + (-1)*k17*((1 - k8)/k8*x8 - x18))/k33,
  diff(x9, t) = (1*k30/k3*x7/(1 + x7/k3 + x7/k4 + x8/k1 + x8/k2) + 1*(k13 + k15)*x11 + (-1)*k17*((1 - k9)/k9*x9 - x13) + 1*k10*x5 + (-1)*k29*x9)/k33,
  diff(x10, t) = (1*k18/k4*x7/(1 + x7/k3 + x7/k4 + x8/k1 + x8/k2) + (-1)*k16*x10 + 1*(k13 + k15)*x12 + (-1)*k17*((1 - k9)/k9*x10 - x14) + 1*k28*x3)/k33,
  diff(x11, t) = (1*k19/k1*x8/(1 + x7/k3 + x7/k4 + x8/k1 + x8/k2) + (-1)*(k13 + k15)*x11 + 1*k5*x4 + (-1)*k17*((1 - k8)/k8*x11 - x15) + (-1)*k11*x11)/k33,
  diff(x12, t) = (1*k20/k2*x8/(1 + x7/k3 + x7/k4 + x8/k1 + x8/k2) + (-1)*(k13 + k15)*x12 + 1*k6*x6 + (-1)*k17*((1 - k8)/k8*x12 - x16) + (-1)*k12*x12)/k33,
  diff(x13, t) = 1*k17*((1 - k9)/k9*x9 - x13)/k33,
  diff(x14, t) = 1*k17*((1 - k9)/k9*x10 - x14)/k33,
  diff(x15, t) = 1*k17*((1 - k8)/k8*x11 - x15)/k33,
  diff(x16, t) = 1*k17*((1 - k8)/k8*x12 - x16)/k33,
  diff(x17, t) = 1*k17*((1 - k9)/k9*x7 - x17)/k33,
  diff(x18, t) = 1*k17*((1 - k8)/k8*x8 - x18)/k33 }