[ Diff(x[1], t) = (1*k[11]*k[1] + (-1)*k[11]*k[2]*x[1]*x[3] + (-1)*k[11]*k[7]*x[1])/k[11],
  Diff(x[2], t) = (1*k[11]*k[2]*x[1]*x[3] + 1*k[11]*k[3]*x[3] + (-1)*k[11]*k[4]*x[2] + (-1)*k[11]*k[8]*x[2])/k[11],
  Diff(x[3], t) = (1*k[11]*k[4]*x[2] + (-1)*k[11]*k[5]*x[3]*x[4] + (-1)*k[11]*k[9]*x[3])/k[11],
  Diff(x[4], t) = (1*k[11]*k[6]*x[3] + (-1)*k[11]*k[10]*x[4])/k[11] ]