Covariant derivative along a curve
See @lee2006riemannian Lemma 4.9.
How can we derive vector fields defined on a curve, with respect to the parameter of the curve?
Given a covariant derivative operator in a manifold , for each curve , determines a unique operator
satisfying the following properties:
(a) Linearity over :
(b) Product rule:
(c) If is extendible, then for any extension of ,
For any , is called the covariant derivative of along .
Local coordinate expression