[ Diff(x[1], t) = (1*k[21]*2060/365 + (-1)*k[21]*1/(2*365)*x[1] + (-1)*k[21]*45685/(439197*30)*x[1]*x[2]/(k[10] + x[2]))/k[21],
  Diff(x[2], t) = (1*k[21]*45685/(439197*30)*x[1]*x[2]/(k[10] + x[2]) + (-1)*k[21]*45682/(439197*30)*x[2] + (-1)*k[21]*1/(2*365)*x[2])/k[21],
  Diff(x[3], t) = (1*k[21]*237/10*k[20]/365000 + (-1)*k[21]*1/(346/5*365)*x[3] + (-1)*k[21]*16/(108*1000000*1825/2)*x[3]*x[2]/(k[11] + x[2]))/k[21],
  Diff(x[4], t) = (1*k[21]*16/(108*1000000*1825/2)*x[3]*x[2]/(k[11] + x[2]) + (-1)*k[21]*6/(108*1000000*1825/2)*x[4] + (-1)*k[21]*1/(346/5*365)*x[4])/k[21] ]