ACQUISTAPACE, F.; BROGLIA, F.; F. FERNANDO, J. On Hilbert’s 17th problem and Pfister’s multiplicative formulae for the ring of real analytic functions. ANNALI SCUOLA NORMALE SUPERIORE - CLASSE DI SCIENZE, [S. l.], v. 13, n. 2, p. 333-369, 2014. DOI: 10.2422/2036-2145.201201_004. Disponível em: https://journals.sns.it/index.php/annaliscienze/article/view/340. Acesso em: 20 feb. 2026.