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