{ diff(x1, t) = 0/k22,
  diff(x2, t) = (1*1/k2*x1 + (-1)*1/k2*x2 + (-1)*k4*365/k9*(x3 + x7)/x1*x2 + (-1)*k7*365/k10*(x4 + x8)/x1*x2 + 1*1/k12*x5 + 1*1/k12*x6 + 1*1/k12*x9)/k22,
  diff(x3, t) = ((-1)*1/k2*x3 + 1*k4*365/k9*(x3 + x7)/x1*x2 + (-1)*365/k9*x3)/k22,
  diff(x4, t) = ((-1)*1/k2*x4 + 1*k7*365/k10*(x4 + x8)/x1*x2 + (-1)*365/k10*x4)/k22,
  diff(x5, t) = ((-1)*1/k2*x5 + (-1)*(1 - k21)*k7*365/k10*(x4 + x8)/x1*x5 + 1*365/k9*x3 + (-1)*1/k12*x5)/k22,
  diff(x6, t) = ((-1)*1/k2*x6 + (-1)*(1 - k21)*k4*365/k9*(x3 + x7)/x1*x6 + 1*365/k10*x4 + (-1)*1/k12*x6)/k22,
  diff(x7, t) = ((-1)*1/k2*x7 + 1*(1 - k21)*k4*365/k9*(x3 + x7)/x1*x6 + (-1)*365/k9*x7)/k22,
  diff(x8, t) = ((-1)*1/k2*x8 + 1*(1 - k21)*k7*365/k10*(x4 + x8)/x1*x5 + (-1)*365/k10*x8)/k22,
  diff(x9, t) = ((-1)*1/k2*x9 + 1*365/k9*x7 + 1*365/k10*x8 + (-1)*1/k12*x9)/k22 }