NAKAI, Mitsuru; SARIO, Leo. Classification and Deformation of Riemannian Spaces. Mathematica Scandinavica, Berkeley, CA, United States, v. 20, p. 193–208, 1967. DOI: 10.7146/math.scand.a-10830. Disponível em: https://journals.msp.org/mscand/article/view/2496. Acesso em: 25 jul. 2026.