@article{MS2_1981__48_166746,
     author = {A.H.M. Hoare},
     title = {Nielsen methods in groups with a length function.},
     journal = {Mathematica Scandinavica},
     pages = {153--164},
     publisher = {mathdoc},
     volume = {48},
     year = {1981},
     zbl = {0463.20023},
     url = {http://geodesic.mathdoc.fr/item/MS2_1981__48_166746/}
}