*   Nterms = 5

L   [A(1,2,3,4)] =

       + ss12^-1 * (
          + chi1*ga(k3)*chi2*e3.e4
          - chi1*ga(e3)*chi2*k3.e4
          + chi1*ga(e4)*chi2*k4.e3
          )

       + ss23^-1 * (
          - chi1*ga(e4)*chi2*k2.e3
          + 1/2*chi1*ga(e4)*ga(e3)*ga(k3)*chi2
          );