“…Applying Lemma 1, one has T (δ i , δ j , ∂ k ) = 0 for every t ≥ 0 if and only if c 1 d 2 3 = 0. Since c 3 (t) = 0 for every t ≥ 0, from the nondegeneracy condition (6) of the metric G it follows that c 1 (t) = 0 for every t ≥ 0, and hence, the expressions (35) of T (δ i , δ j , ∂ k ) and (32) of T (∂ i , ∂ j , ∂ k ) vanish simultaneously if and only if d 3 = 0, i.e., the metric is of natural diagonal lift type. We compute the other components of the tensor field T with resect to the adapted local frame field {δ i , ∂ j } n i,j=1 by imposing the conditions already obtained, that is c 3 = d 3 = 0 and the locally flatness of the base manifold, and we have that:…”