{ diff(x1, t) = (1*k11*(k1*x1*(1 - k2*x1) + k9*x1*x3) + (-1)*k11*k3*x1*x2)/k11,
  diff(x2, t) = (1*k11*(k4*x2*(1 - k5*x2) + k6*x1*x2) + (-1)*k11*k10*x2*x3)/k11,
  diff(x3, t) = (1*k11*k7 + (-1)*k11*k8*x3)/k11 }