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@article{CM_1971__23_3_347_0, author = {Beidleman, James C.}, title = {Formations and $\pi $-closure in finite groups}, journal = {Compositio Mathematica}, pages = {347--356}, publisher = {Wolters-Noordhoff Publishing}, volume = {23}, number = {3}, year = {1971}, zbl = {0228.20009}, language = {en}, url = {http://geodesic.mathdoc.fr/item/CM_1971__23_3_347_0/} }
Beidleman, James C. Formations and $\pi $-closure in finite groups. Compositio Mathematica, Tome 23 (1971) no. 3, pp. 347-356. http://geodesic.mathdoc.fr/item/CM_1971__23_3_347_0/