@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://www.numdam.org/item/CM_1971__23_3_347_0/}
}