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@article{MZ_1986__192_173726, author = {S.M. Gersten}, title = {Products of {Conjugacy} {Classes} in a {Free} {Group:} a {Counterexample.}}, journal = {Mathematische Zeitschrift}, pages = {167--182}, publisher = {mathdoc}, volume = {192}, year = {1986}, zbl = {0601.20034}, url = {http://geodesic.mathdoc.fr/item/MZ_1986__192_173726/} }
S.M. Gersten. Products of Conjugacy Classes in a Free Group: a Counterexample.. Mathematische Zeitschrift, Tome 192 (1986), pp. 167-182. http://geodesic.mathdoc.fr/item/MZ_1986__192_173726/