@article{PM_1994_1994_1_a21,
     author = {Levitt, Gilbert},
     title = {Arboles-R y el invariante {Bieri-Neumann-Strebel.}},
     journal = {Publicacions matem\`atiques},
     pages = {195-202},
     publisher = {mathdoc},
     volume = {38},
     number = {1},
     year = {1994},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/PM_1994_1994_1_a21/}
}