@article{CMUC_1988__29_4_a5,
     author = {Engelking, Ryszard},
     title = {An elementary proof of {Noble's} theorem on normality of powers},
     journal = {Commentationes Mathematicae Universitatis Carolinae},
     pages = {677--678},
     publisher = {mathdoc},
     volume = {29},
     number = {4},
     year = {1988},
     mrnumber = {982785},
     zbl = {0665.54016},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/CMUC_1988__29_4_a5/}
}