{ diff(x1, t) = 1*k3*(k7*x5 - k6*x1*x6)/k3/k3,
  diff(x2, t) = (-1)*k3*(k13*x2*x8 - k12*x3)/k3/k3,
  diff(x3, t) = ((-1)*k3*(k9*x3 - k8*x4)/k3 + 1*k3*(k13*x2*x8 - k12*x3)/k3)/k3,
  diff(x4, t) = ((-1)*k3*(k5*x4 - k4*x5)/k3 + 1*k3*(k9*x3 - k8*x4)/k3)/k3,
  diff(x5, t) = (1*k3*(k5*x4 - k4*x5)/k3 + (-1)*k3*(k7*x5 - k6*x1*x6)/k3)/k3,
  diff(x6, t) = (1*k3*(k7*x5 - k6*x1*x6)/k3 + (-1)*k3*(k11*x6 - k10*x7*x8)/k3)/k3,
  diff(x7, t) = 1*k3*(k11*x6 - k10*x7*x8)/k3/k3,
  diff(x8, t) = (1*k3*(k11*x6 - k10*x7*x8)/k3 + (-1)*k3*(k13*x2*x8 - k12*x3)/k3)/k3 }