@article{10_1017_S0017089500001634,
     author = {Wohlfahrt, Klaus},
     title = {A direct proof of {Leutbecher's} {Lemma}},
     journal = {Glasgow mathematical journal},
     pages = {179--180},
     year = {1972},
     volume = {13},
     number = {2},
     doi = {10.1017/S0017089500001634},
     url = {http://geodesic.mathdoc.fr/articles/10.1017/S0017089500001634/}
}