@article{1028998143, author = {Lyndon, R. C.}, title = {The equation $a^2b^2=c^2$ in free groups.}, journal = {Michigan Math. J.}, volume = {6}, number = {1}, year = {1959}, pages = { 89-95}, language = {en}, url = {http://dml.mathdoc.fr/item/1028998143} }
Lyndon, R. C. The equation $a^2b^2=c^2$ in free groups.. Michigan Math. J., Tome 6 (1959) no. 1, pp. 89-95. http://gdmltest.u-ga.fr/item/1028998143/