@article{10_2140_agt_2009_9_327,
     author = {Louder, Larsen and McReynolds, D B},
     title = {Graphs of subgroups of free groups},
     journal = {Algebraic and Geometric Topology},
     pages = {327--335},
     year = {2009},
     volume = {9},
     number = {1},
     doi = {10.2140/agt.2009.9.327},
     url = {http://geodesic.mathdoc.fr/articles/10.2140/agt.2009.9.327/}
}