@article{MZ_1972__129_171832,
     author = {Istv\'an Beck},
     title = {Projective and {Free} {Modules.}},
     journal = {Mathematische Zeitschrift},
     pages = {231--234},
     publisher = {mathdoc},
     volume = {129},
     year = {1972},
     zbl = {0236.16020},
     url = {http://geodesic.mathdoc.fr/item/MZ_1972__129_171832/}
}