@article{MZ_1978__158_172621,
     author = {Norbert Peczynski and Wolfram Reiwer},
     title = {On {Cancellations} in {HNN-Groups.}},
     journal = {Mathematische Zeitschrift},
     pages = {79--86},
     publisher = {mathdoc},
     volume = {158},
     year = {1978},
     zbl = {0352.20025},
     url = {http://geodesic.mathdoc.fr/item/MZ_1978__158_172621/}
}