\(\left[ {\overrightarrow {{u_1}} ,\overrightarrow {{u_2}} } \right] = \left[ {\overrightarrow {{u_2}} ,\overrightarrow {{u_1}} } \right]\)                         

\(\left[ {\overrightarrow {{u_1}} ,\overrightarrow {{u_2}} } \right] =  - \left[ {\overrightarrow {{u_2}} ,\overrightarrow {{u_1}} } \right]\)

\(\left[ {\overrightarrow {{u_1}} ,\overrightarrow {{u_2}} } \right] - \left[ {\overrightarrow {{u_2}} ,\overrightarrow {{u_1}} } \right] = \overrightarrow 0 \)  

\(\left[ {\overrightarrow {{u_1}} ,\overrightarrow {{u_2}} } \right] + \left[ {\overrightarrow {{u_2}} ,\overrightarrow {{u_1}} } \right] = 0\)