GILKEY, P. B. Local invariants of a pseudo-Riemannian manifold. MATHEMATICA SCANDINAVICA, [S. l.], v. 36, p. 109–130, 1975. DOI: 10.7146/math.scand.a-11566. Disponível em: https://www.mscand.dk/article/view/11566. Acesso em: 2 may. 2024.