Acquistapace, Francesca, Fabrizio Broglia, and José F. Fernando. 2014. “On Hilbert’s 17th Problem and Pfister’s Multiplicative Formulae for the Ring of Real Analytic Functions”. ANNALI SCUOLA NORMALE SUPERIORE - CLASSE DI SCIENZE 13 (2):333-69. https://doi.org/10.2422/2036-2145.201201_004.