@article{PIM_1983_N_S_33_47_a11,
     author = {C. H. Heiberg},
     title = {Level {Sets} of {Polynomials} in {Several} {Real} {Variables}},
     journal = {Publications de l'Institut Math\'ematique},
     pages = {83 },
     publisher = {mathdoc},
     volume = {_N_S_33},
     number = {47},
     year = {1983},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/PIM_1983_N_S_33_47_a11/}
}