@article{10_4064_aa_9_1_79_82,
     author = {J. Cassels},
     title = {On the representation of rational functions as sums of squares},
     journal = {Acta Arithmetica},
     pages = {79--82},
     publisher = {mathdoc},
     volume = {9},
     number = {1},
     year = {1964},
     doi = {10.4064/aa-9-1-79-82},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/aa-9-1-79-82/}
}