I have a question about the answer to this question
I don't know how to get the second equality in
$$\nabla_{E_i} E_j (\gamma(t)) = \nabla_{\gamma'} E_j (\gamma(t)) = 0$$
I tried to use the fact that the covariant derivative of the geodesic $\gamma$ is zero and to write the tangent vector along the curve in terms of the $E_j$'s but it doesn't work out.