@article{10_4171_ggd_170,
     author = {Fran\c{c}ois Gautero},
     title = {A non-trivial example of a free-by-free group    with the {Haagerup} property},
     journal = {Groups, geometry, and dynamics},
     pages = {677--699},
     year = {2012},
     volume = {6},
     number = {4},
     doi = {10.4171/ggd/170},
     url = {http://geodesic.mathdoc.fr/articles/10.4171/ggd/170/}
}