@article{CMH_1982__57_139914,
     author = {M.-A. Knus and R. Parimala and M. Ojanguren},
     title = {Positive-definite quadratic bundles over the plane.},
     journal = {Commentarii mathematici Helvetici},
     pages = {400--411},
     publisher = {mathdoc},
     volume = {57},
     year = {1982},
     zbl = {0507.14010},
     url = {http://geodesic.mathdoc.fr/item/CMH_1982__57_139914/}
}