@article{GDZPPN002068346,
title = {Covering homotopy 3-spheres.},
journal = {Commentarii mathematici Helvetici},
volume = {67},
year = {1992},
pages = {287-292},
zbl = {0759.57002},
url = {http://dml.mathdoc.fr/item/GDZPPN002068346}
}
Piergallini, R. Covering homotopy 3-spheres.. Commentarii mathematici Helvetici, Tome 67 (1992) pp. 287-292. http://gdmltest.u-ga.fr/item/GDZPPN002068346/