@article{1029000641, author = {Hill, Paul}, title = {The covering theorem for upper basic subgroups.}, journal = {Michigan Math. J.}, volume = {18}, number = {1}, year = {1971}, pages = { 187-192}, language = {en}, url = {http://dml.mathdoc.fr/item/1029000641} }
Hill, Paul. The covering theorem for upper basic subgroups.. Michigan Math. J., Tome 18 (1971) no. 1, pp. 187-192. http://gdmltest.u-ga.fr/item/1029000641/