{ diff(x1, t) = (1*k1*k11 + (-1)*k2*x1*x6*1/1000 + (-2)*k3*x1*(x1 - 1)*1/2 + 2*k4*x2 + (-1)*k7*x1*x3^2/(k8^2 + x3^2) + 1*k5*x3)/k10,
  diff(x2, t) = (1*k3*x1*(x1 - 1)*1/2 + (-1)*k4*x2 + (-2)*k6*x2*(x2 - 1)*1/2)/k10,
  diff(x3, t) = (4*k6*x2*(x2 - 1)*1/2 + 1*k7*x1*x3^2/(k8^2 + x3^2) + (-1)*k5*x3)/k10,
  diff(x4, t) = 0,
  diff(x5, t) = 0,
  diff(x6, t) = (-1)*k9*x6/k10 }