@article{GDZPPN002101858,
title = {Smoothness and analycity for solutions of first order systems of partial differential equations on nilpotent Lie groups.},
journal = {Inventiones mathematicae},
volume = {82},
year = {1985},
pages = {205-216},
zbl = {0588.35087},
url = {http://dml.mathdoc.fr/item/GDZPPN002101858}
}
Corwin, Lawrence.; Helffer, B. Smoothness and analycity for solutions of first order systems of partial differential equations on nilpotent Lie groups.. Inventiones mathematicae, Tome 82 (1985) pp. 205-216. http://gdmltest.u-ga.fr/item/GDZPPN002101858/