@article{1183522558,
author = {Shapiro, Arnold and Whitehead, J. H. C.},
title = {A proof and extension of Dehn's lemma},
journal = {Bull. Amer. Math. Soc.},
volume = {64},
number = {6},
year = {1958},
pages = { 174-178},
language = {en},
url = {http://dml.mathdoc.fr/item/1183522558}
}
Shapiro, Arnold; Whitehead, J. H. C. A proof and extension of Dehn's lemma. Bull. Amer. Math. Soc., Tome 64 (1958) no. 6, pp. 174-178. http://gdmltest.u-ga.fr/item/1183522558/