@article{10_4171_ggd_89,
     author = {Lewis Bowen},
     title = {The ergodic theory of free group actions:  entropy and the $f$-invariant},
     journal = {Groups, geometry, and dynamics},
     pages = {419--432},
     year = {2010},
     volume = {4},
     number = {3},
     doi = {10.4171/ggd/89},
     url = {http://geodesic.mathdoc.fr/articles/10.4171/ggd/89/}
}