11

$${\boldsymbol{(s_1, s_2) \equiv s_1 s_2 – s_2 s_1 = }i\hbar \boldsymbol{s_3, (s_3, s_1) = }i \hbar \boldsymbol{s_2, (s_2, s_3) = }i\hbar \boldsymbol{s_1}.}$$