The L 1-Sobolev inequality states that the L n/(n--1)-norm of a compactly
supported function on Euclidean n-space is controlled by the L 1-norm of its
gradient. The generalization to differential forms (due to Lanzani & Stein and
Bourgain & Brezis) is recent, and states that a the L n/(n--1)-norm of a
compactly supported differential h-form is controlled by the L 1-norm of its
exterior differential du and its exterior codifferential δu (in special
cases the L 1-norm must be replaced by the H 1-Hardy norm). We shall extend
this result to Heisenberg groups in the framework of an appropriate complex of
differential forms