@article{GDZPPN002212641,
title = {Minimal bi-invariant Hilbert subspaces of distributions on nilpotent Lie groups.},
journal = {Journal f\"ur die reine und angewandte Mathematik},
volume = {468},
year = {1995},
pages = {159-168},
zbl = {0820.46035},
url = {http://dml.mathdoc.fr/item/GDZPPN002212641}
}
Pestman, Wiebe R. Minimal bi-invariant Hilbert subspaces of distributions on nilpotent Lie groups.. Journal für die reine und angewandte Mathematik, Tome 468 (1995) pp. 159-168. http://gdmltest.u-ga.fr/item/GDZPPN002212641/