@article{10_4171_ggd_49,
     author = {Russell Lyons and Mika\"el Pichot and St\'ephane Vassout},
     title = {Uniform non-amenability, cost, and the first $\ell^2${-Betti} number},
     journal = {Groups, geometry, and dynamics},
     pages = {595--617},
     year = {2008},
     volume = {2},
     number = {4},
     doi = {10.4171/ggd/49},
     url = {http://geodesic.mathdoc.fr/articles/10.4171/ggd/49/}
}