@article{JEMS_2008_10_3_a7,
     author = {Laurent Bartholdi and Markus Neuhauser and Wolfgang Woess},
     title = {Horocyclic products of trees},
     journal = {Journal of the European Mathematical Society},
     pages = {771--816},
     publisher = {mathdoc},
     volume = {10},
     number = {3},
     year = {2008},
     doi = {10.4171/jems/130},
     url = {http://geodesic.mathdoc.fr/articles/10.4171/jems/130/}
}