@article{DOCMA_2012__S3__a3,
     author = {Schm\"udgen, Konrad},
     title = {Around {Hilbert's} 17th problem},
     journal = {Documenta mathematica},
     pages = {433--438},
     publisher = {mathdoc},
     volume = {Optimization Stories},
     year = {2012},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/DOCMA_2012__S3__a3/}
}