@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/}
}