@article{JRAM_1991__416_153321,
     author = {D. M\"uller},
     title = {A new criterion for local non-solvability of homogeneous left invariant differential operators on nilpotent {Lie} groups.},
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {207--219},
     publisher = {mathdoc},
     volume = {416},
     year = {1991},
     zbl = {0716.22003},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1991__416_153321/}
}