{ diff(x1, t) = (1*k9*k10*k11^k12*k13/(k11^k12 + x3^k12) + (-1)*k9*k14*x1)/k9,
  diff(x2, t) = (1*k9*k15*x1*k16/(k16 + x3) + (-1)*k9*k17*x2/(k18 + x2) + (-1)*k9*k19*x2)/k9 }