POLETAEVA, E. Penrose’s tensors. II. MATHEMATICA SCANDINAVICA, [S. l.], v. 72, p. 191–211, 1993. DOI: 10.7146/math.scand.a-12444. Disponível em: https://www.mscand.dk/article/view/12444. Acesso em: 8 may. 2024.