CHRISTENSEN, E.; IVAN, C. Sums of two-dimensional spectral triples. MATHEMATICA SCANDINAVICA, [S. l.], v. 100, n. 1, p. 35–60, 2007. DOI: 10.7146/math.scand.a-15015. Disponível em: https://www.mscand.dk/article/view/15015. Acesso em: 3 may. 2024.