@article{PMFA_1982_27_2_a3,
     author = {K\"onigsdorf, Helga},
     title = {Lemma 1},
     journal = {Pokroky matematiky, fyziky a astronomie},
     pages = {101--106},
     year = {1982},
     volume = {27},
     number = {2},
     language = {cs},
     url = {http://geodesic.mathdoc.fr/item/PMFA_1982_27_2_a3/}
}