@article{MAN_1980__253_163479,
     author = {Y. Ershov and M. Fried},
     title = {Frattini {Covers} and {Projective} {Groups} {Without} the {Extension} {Property.}},
     journal = {Mathematische Annalen},
     pages = {233--240},
     publisher = {mathdoc},
     volume = {253},
     year = {1980},
     zbl = {0475.20021},
     url = {http://geodesic.mathdoc.fr/item/MAN_1980__253_163479/}
}