@article{GT_2009_13_3_a13,
     author = {Kapovich, Ilya and Lustig, Martin},
     title = {Geometric intersection number and analogues of the curve complex for free groups},
     journal = {Geometry & topology},
     pages = {1805--1833},
     publisher = {mathdoc},
     volume = {13},
     number = {3},
     year = {2009},
     doi = {10.2140/gt.2009.13.1805},
     url = {http://geodesic.mathdoc.fr/articles/10.2140/gt.2009.13.1805/}
}