{ diff(x1, t) = ((-1)*(k1*x1*k9 - k5*x2*k10) + (-1)*k2*x2^k3/(k4^k3 + x2^k3)*x1*k9)/k10,
  diff(x2, t) = (1*k8*k9 + 1*(k1*x1*k9 - k5*x2*k10) + (-1)*k6*x2*k11 + 1*k2*x2^k3/(k4^k3 + x2^k3)*x1*k9)/k9 }