{ diff(x1, t) = 1*k9*((-x1)/k6 + k5*k4/k6)/k9,
  diff(x2, t) = 1*k9*((-x2)/k8 + k7*k4/k8)/k9,
  diff(x3, t) = 1*k9*(k10*x10 - k11*x3 - k12*x4*x3)/k9,
  diff(x4, t) = 1*k9*k13*x3/k9,
  diff(x5, t) = 1*k9*(k14*x3 - k15*x5)/k9,
  diff(x6, t) = 1*k9*((x3*x5)^k17/(k16^k17 + (x3*x5)^k17) - k1*x6)/k9,
  diff(x7, t) = 1*k9*(k20*x9 - k19*x7 - k2*x7*x10 + k3*x8)/k9,
  diff(x8, t) = 1*k9*(k2*x7*x10 - k21*x8 - k3*x8)/k9,
  diff(x9, t) = 1*k9*(k1*x6 - k18*x9)/k9 }