Michalska, Maria. “Real Nullstellensatz and Sums of Squares”. In Analitic and Algebraic Geometry 4, edited by Tadeusz Krasiński and Stanisław Spodzieja, 121–136. Poland: Lodz University Press, 2022. Accessed January 21, 2026. https://www.press.uni.lodz.pl/index.php/wul/catalog/book/1259/chapter/3684.