@article{10_1090_S0894_0347_09_00634_1,
     author = {Calegari, Danny},
     title = {Stable commutator length is rational in free groups},
     journal = {Journal of the American Mathematical Society},
     pages = {941--961},
     year = {2009},
     volume = {22},
     number = {4},
     doi = {10.1090/S0894-0347-09-00634-1},
     url = {http://geodesic.mathdoc.fr/articles/10.1090/S0894-0347-09-00634-1/}
}