@article{CM_1993__86_2_235_0,
     author = {Colliot-Th\'el\`ene, J.-L.},
     title = {The {Noether-Lefschetz} theorem and sums of 4 squares in the rational function field $R(x, y)$},
     journal = {Compositio Mathematica},
     pages = {235--243},
     publisher = {Kluwer Academic Publishers},
     volume = {86},
     number = {2},
     year = {1993},
     mrnumber = {1214459},
     zbl = {0774.12002},
     language = {en},
     url = {http://www.numdam.org/item/CM_1993__86_2_235_0/}
}