  Recently, penalties promoting signals that are sparse within and across
groups have been proposed. In this letter, we propose a generalization that
allows to encode more intricate dependencies within groups. However, this
complicates the realization of the threshold function associated with the
penalty, which hinders the use of the penalty in energy minimization. We
discuss how to sidestep this problem, and demonstrate the use of the modified
penalty in an energy minimization formulation for an inverse problem.
