@article{700990,
     title = {Topologische Untergruppenra\"ume},
     booktitle = {General Topology and its Relations to Modern Analysis and Algebra},
     series = {GDML\_Books},
     publisher = {Academia Publishing House of the Czechoslovak Academy of Sciences},
     address = {Praha},
     year = {1962},
     pages = {196-198},
     mrnumber = {MR0173727},
     zbl = {0111.31103},
     url = {http://dml.mathdoc.fr/item/700990}
}

Helmberg, G. Topologische Untergruppenraüme, dans General Topology and its Relations to Modern Analysis and Algebra, GDML_Books,  (1962), pp. 196-198. http://gdmltest.u-ga.fr/item/700990/