@article{MZ_1991__206_1_174227,
     author = {Robert W. Fitzgerald},
     title = {Picard groups of {Witt} rings.},
     journal = {Mathematische Zeitschrift},
     pages = {303--320},
     publisher = {mathdoc},
     volume = {206},
     number = {1},
     year = {1991},
     zbl = {0702.11024},
     url = {http://geodesic.mathdoc.fr/item/MZ_1991__206_1_174227/}
}