A coefficient which gives the difference between partial derivatives of two coordinates with respect to the other coordinate,
![\begin{displaymath}
c_{\alpha\beta}^\mu \vec e_\mu = [\vec e_\alpha, \vec e_\beta] = \nabla_\alpha\vec e_\beta-\nabla_\beta \vec e_\alpha.
\end{displaymath}](c2_645.gif){kind=small}