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@article{MZ_1991__206_1_174214, author = {Zeng Guangxin}, title = {On preordered fields related to {Hilbert's} 17th problem.}, journal = {Mathematische Zeitschrift}, pages = {145--152}, publisher = {mathdoc}, volume = {206}, number = {1}, year = {1991}, zbl = {0691.12009}, url = {http://geodesic.mathdoc.fr/item/MZ_1991__206_1_174214/} }
Zeng Guangxin. On preordered fields related to Hilbert's 17th problem.. Mathematische Zeitschrift, Tome 206 (1991) no. 1, pp. 145-152. http://geodesic.mathdoc.fr/item/MZ_1991__206_1_174214/