@article{03888036,
title = {Level sets of polynomials in several real variables.},
journal = {Publications de l'Institut Math\'ematique. Nouvelle S\'erie},
volume = {33(47)},
year = {1983},
pages = {83-87},
zbl = {0557.31003},
language = {en},
url = {http://dml.mathdoc.fr/item/03888036}
}
Heiberg, C.H. Level sets of polynomials in several real variables.. Publications de l'Institut Mathématique. Nouvelle Série, Tome 33(47) (1983) pp. 83-87. http://gdmltest.u-ga.fr/item/03888036/