Acquistapace, F., Broglia, F., & F. Fernando, J. (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), 333-369. https://doi.org/10.2422/2036-2145.201201_004
