@article{10_4064_sm148_1_8,
     author = {Detlef M\"uller and Zhenqiu Zhang},
     title = {A class of solvable non-homogeneous differential operators
on the {Heisenberg} group},
     journal = {Studia Mathematica},
     pages = {87--96},
     publisher = {mathdoc},
     volume = {148},
     number = {1},
     year = {2001},
     doi = {10.4064/sm148-1-8},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/sm148-1-8/}
}