{ diff(x1, t) = (-1)*k1*(k2*x1*x2 - k3*x7)/k1,
  diff(x2, t) = ((-1)*k1*(k2*x1*x2 - k3*x7) + 1*k1*k4 + (-1)*k1*k5*x2)/k1,
  diff(x3, t) = (1*k1*k6*x5*x4 + (-1)*k1*k7*x7*x3)/k1,
  diff(x4, t) = ((-1)*k1*k6*x5*x4 + 1*k1*k7*x7*x3)/k1,
  diff(x5, t) = ((-1)*k1*k6*x5*x4 + 1*k1*k9*x6)/k1,
  diff(x6, t) = (1*k1*k7*x7*x3 + (-1)*k1*k9*x6)/k1,
  diff(x7, t) = (1*k1*(k2*x1*x2 - k3*x7) + (-1)*k1*k8*x7)/k1 }