@article{AM2_1977__16_136690,
     author = {Stefan Czerwik},
     title = {Multi-valued contraction mappings in metric spaces. {(Short} {Communication).}},
     journal = {Aequationes mathematicae},
     pages = {188--189},
     publisher = {mathdoc},
     volume = {16},
     year = {1977},
     zbl = {0385.54027},
     url = {http://geodesic.mathdoc.fr/item/AM2_1977__16_136690/}
}