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: http://20.103.181.36/index.php/annaliscienze/article/view/340. Acesso em: 28 may. 2025.