@article{10_4171_ggd_124,
     author = {Mikl\'os Ab\'ert and Andrei Jaikin-Zapirain and Nikolay Nikolov},
     title = {The rank gradient from a combinatorial viewpoint},
     journal = {Groups, geometry, and dynamics},
     pages = {213--230},
     year = {2011},
     volume = {5},
     number = {2},
     doi = {10.4171/ggd/124},
     url = {http://geodesic.mathdoc.fr/articles/10.4171/ggd/124/}
}