@article{10_4064_aa98_2_9,
     author = {E. Victor Flynn and Joseph L. Wetherell},
     title = {Covering collections
and a challenge problem of {Serre}},
     journal = {Acta Arithmetica},
     pages = {197--205},
     publisher = {mathdoc},
     volume = {98},
     number = {2},
     year = {2001},
     doi = {10.4064/aa98-2-9},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/aa98-2-9/}
}