@article{MAN_1996__305_2_182993,
     author = {D. M\"uller and T. Coulhon and J. Zienkiewicz},
     title = {About {Riesz} transforms on the {Heisenberg} groups.},
     journal = {Mathematische Annalen},
     pages = {369--380},
     publisher = {mathdoc},
     volume = {305},
     number = {2},
     year = {1996},
     zbl = {0859.22006},
     url = {http://geodesic.mathdoc.fr/item/MAN_1996__305_2_182993/}
}