We show that divergence free vector fields which belong to L^1 on stratified,
nilpotent groups are in the dual space of functions whose sub-gradient are L^Q
integrable where Q is the homogeneous dimension of the group. This was first
obtained on Euclidean space by Bourgain and Brezis.Comment: 15 pages, v2 has some typos fixed in lemma 2.
