GILKEY, Peter B. Local invariants of a pseudo-Riemannian manifold. Mathematica Scandinavica, Berkeley, CA, United States, v. 36, p. 109–130, 1975. DOI: 10.7146/math.scand.a-11566. Disponível em: https://journals.msp.org/mscand/article/view/2050. Acesso em: 25 jul. 2026.