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@article{MZ_1968__106_171021, author = {John Cossey}, title = {On a {Problem} of {Hanna} {Neumann.}}, journal = {Mathematische Zeitschrift}, pages = {187--190}, publisher = {mathdoc}, volume = {106}, year = {1968}, zbl = {0174.04702}, url = {http://geodesic.mathdoc.fr/item/MZ_1968__106_171021/} }
John Cossey. On a Problem of Hanna Neumann.. Mathematische Zeitschrift, Tome 106 (1968), pp. 187-190. http://geodesic.mathdoc.fr/item/MZ_1968__106_171021/