{ diff(x1, t) = 0,
  diff(x2, t) = 0,
  diff(x3, t) = 0,
  diff(x4, t) = (1*k1*(k2*k51/k3*k52/k4 - k5*k53/k6*x4/k7)/((1 + k51/k3 + k53/k6)*(1 + k52/k4 + x4/k7)) + (-1)*k1*(k8*x4/k9 - k10*x5/k11)/(1 + x4/k9 + x5/k11))/k1,
  diff(x5, t) = (1*k1*(k8*x4/k9 - k10*x5/k11)/(1 + x4/k9 + x5/k11) + (-1)*k1*(k12*x5/k13 - k14*x6/k15)/(1 + x5/k13 + x6/k15) + (-1)*k1*(k36*x5/k37 - k38*x8/k39*x11/k40)/(1 + x5/k37 + x8/k39 + x11/k40 + x5/k37*x8/k39 + x8/k39*x11/k40))/k1,
  diff(x6, t) = (1*k1*(k12*x5/k13 - k14*x6/k15)/(1 + x5/k13 + x6/k15) + (-1)*k1*(k16*x6/k17 - k18*x7/k19)/(1 + x6/k17 + x7/k19) + (-1)*k1*341/10000*(k47*x5/k48 - k49*x6/k50)/(1 + x5/k48 + x6/k50))/k1,
  diff(x7, t) = (1*k1*(k16*x6/k17 - k18*x7/k19)/(1 + x6/k17 + x7/k19) + (-1)*k1*(k20*x7/k21 - k22*x8/k23)/(1 + x7/k21 + x8/k23))/k1,
  diff(x8, t) = (1*k1*(k20*x7/k21 - k22*x8/k23)/(1 + x7/k21 + x8/k23) + (-1)*k1*(k24*x8/k25 - k26*x9/k27)/(1 + x8/k25 + x9/k27) + 1*k1*(k36*x5/k37 - k38*x8/k39*x11/k40)/(1 + x5/k37 + x8/k39 + x11/k40 + x5/k37*x8/k39 + x8/k39*x11/k40))/k1,
  diff(x9, t) = (1*k1*(k24*x8/k25 - k26*x9/k27)/(1 + x8/k25 + x9/k27) + (-1)*k1*(k28*x9/k29 - k30*x10/k31)/(1 + x9/k29 + x10/k31))/k1,
  diff(x10, t) = (1*k1*(k28*x9/k29 - k30*x10/k31)/(1 + x9/k29 + x10/k31) + (-1)*k1*(k32*x10/k33 - k34*k52/k35)/(1 + x10/k33 + k52/k35) + 1*k1*(k41*x11/k42*k51/k43 - k44*x10/k45*k53/k46)/((1 + x11/k42 + x10/k45)*(1 + k51/k43 + k53/k46)))/k1,
  diff(x11, t) = (1*k1*(k36*x5/k37 - k38*x8/k39*x11/k40)/(1 + x5/k37 + x8/k39 + x11/k40 + x5/k37*x8/k39 + x8/k39*x11/k40) + (-1)*k1*(k41*x11/k42*k51/k43 - k44*x10/k45*k53/k46)/((1 + x11/k42 + x10/k45)*(1 + k51/k43 + k53/k46)))/k1,
  diff(x12, t) = 0 }