1. [Be] Becker, E.: Hereditarily pythagorean fields and orderings of higher level. IMPA Lecture Notes29, 1978
2. [Be-A] Becker, E., Andradas, C.: On the real stability index of rings and its application to semialgebraic geometry. Sem. Logique et Algèbre Réelle Paris VII, 1984/85
3. [Be-Brö] Becker, E., Bröcker, L.: On the description of the reduced With ring. J. Algebra52, 328?346 (1978)
4. [Be-Kö] Becker, E., Köpping, E.: Reduzierte quadratische Formen und Semiordnungen reeller Körper. Abh. Math. Semin. Univ. Hamb.46, 143?177 (1977)
5. [B-C-R] Bochnak, J., Coste, M., Roy, M.F.: Géométrie Algébrique Réelle. Ergeb. Math., Berlin Heidelberg New York: Springer 1987