@article{GDZPPN002212757,
title = {Analysis of second order differential operators with complex coefficients on the Heisenberg group.},
journal = {Journal f\"ur die reine und angewandte Mathematik},
volume = {468},
year = {1995},
pages = {67-96},
zbl = {0826.43004},
url = {http://dml.mathdoc.fr/item/GDZPPN002212757}
}
Ricci, F.; De Mari, F.; Peloso, M.M. Analysis of second order differential operators with complex coefficients on the Heisenberg group.. Journal für die reine und angewandte Mathematik, Tome 468 (1995) pp. 67-96. http://gdmltest.u-ga.fr/item/GDZPPN002212757/