{ diff(x1, t) = 0,
  diff(x2, t) = ((-1)*k2*x2*k29/(k28 + x2) + 1*k3*x3*k31/(k30 + x3) + 1*k2*(x4*k36*k71 - k37*x2) + (-1)*k2*x2*k46 + (-1)*k2*x2*k66/(x2 + k67))/k2,
  diff(x3, t) = (1*k2*x2*k29/(k28 + x2) + (-1)*k3*x3*k31/(k30 + x3) + (-1)*k3*x3*k48 + (-1)*k3*x3*k68/(x3 + k69))/k3,
  diff(x4, t) = ((-1)*k2*(x4*k36*k71 - k37*x2) + 1*k2*x5*k41 + (-1)*k2*x4*k47 + (-1)*k2*x4*k64/(x4 + k65))/k2,
  diff(x5, t) = (1*k2*(k23 + (k22 + (x9/k21)^k20)*k25/(1 + k22 + (x9/k21)^k20 + (x3/k24)^k26)) + (-1)*k1*x5*k27 + (-1)*k2*x5*k62/(x5 + k63))/k2,
  diff(x6, t) = ((-1)*k2*(x6*x10*k38 - k39*x8) + 1*k2*k42*x7 + (-1)*k1*k43*x6 + (-1)*k2*k52*k72*x6/(k53 + x6))/k2,
  diff(x7, t) = (1*k2*(k7 + (k6 + (x3/k5)^k4)*k9/(1 + k6 + (x3/k5)^k4 + (x9/k8)^k10)) + (-1)*k2*k11*x7 + (-1)*k2*k50*x7/(k51 + x7))/k2,
  diff(x8, t) = (1*k3*x9*k33/(k32 + x9) + (-1)*k2*x8*k35/(k34 + x8) + 1*k2*(x6*x10*k38 - k39*x8) + (-1)*k2*k44*x8 + (-1)*k2*k58*x8/(k59 + x8))/k2,
  diff(x9, t) = ((-1)*k3*x9*k33/(k32 + x9) + 1*k2*x8*k35/(k34 + x8) + (-1)*k3*k45*x9 + (-1)*k3*k60*x9/(k61 + x9))/k3,
  diff(x10, t) = ((-1)*k2*(x6*x10*k38 - k39*x8) + 1*k2*k40*x11 + (-1)*k2*k49*x10 + (-1)*k2*k56*x10/(k57 + x10))/k2,
  diff(x11, t) = (1*k2*(k15 + (k14 + (x3/k13)^k12)*k17/(1 + k14 + (x3/k13)^k12 + (x9/k16)^k18)) + (-1)*k1*k19*x11 + (-1)*k2*k54*x11/(k55 + x11))/k2,
  diff(x12, t) = 0,
  diff(x13, t) = 0 }