Geometric factors for k=0,1,2.
\[\begin{split}G(J_i, J_j, J_k, J_l; k) = (2k+1)\begin{Bmatrix} k & k & 0\\ J_i & J_i & J_k \end{Bmatrix} \begin{Bmatrix} 1 & 1 & k\\ J_k & J_i & J_j \end{Bmatrix} \begin{Bmatrix} 1 & 1 & k\\ J_k & J_i & J_l \end{Bmatrix}.\end{split}\]
