*   Nterms =  6

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

       + ss12^-1 * (
          + chi1*ga(k2)*chi3*e2.e4
          - chi1*ga(e2)*chi3*k2.e4
          - chi1*ga(e4)*chi3*k1.e2
          - 1/2*chi1*ga(e4)*ga(e2)*ga(k2)*chi3
          )

       + ss23^-1 * (
          + chi1*ga(e4)*chi3*k3.e2
          - 1/2*chi1*ga(e4)*ga(e2)*ga(k2)*chi3
          );