{\displaystyle {j}}={\vec {l}}+{\vec {s}},\;{\vec {s}}\cdot {\vec {l}}={1 \vec {j^{2}}}-{\vec {l}}^{2}-{\vec {s}}^{2})}
{\displaystyle {\vec {j}}={\vec {l}}+{\vec {s}},\;{\vec {s}}\cdot {\vec {l}}={1 \over 2}({\vec {j^{2}}}-{\vec {l}}^{2}-{\vec {s}}^{2})}