@article{MM2_1987__58_155209,
     author = {M\'onica Clapp and Luis Montejano},
     title = {Lusternik-Schnirelmann category and minimal coverings with contractible sets.},
     journal = {Manuscripta mathematica},
     pages = {37--46},
     publisher = {mathdoc},
     volume = {58},
     year = {1987},
     zbl = {0643.55002},
     url = {http://geodesic.mathdoc.fr/item/MM2_1987__58_155209/}
}