Yes, I know that. But \nabla_{\partial_j}R_{ilkm}=(\nabla_{\partial_j}R)(\partial_i,\partial_l,\partial_k,\partial_m) How can the contraction really happen?(since \nabla_a g_{bc}=0 means (\nabla_a g)(\partial_b,\partial_c)=0)
Would you like to give me more detail? Thank you!