  We study the eigenvalues and eigenfunctions of the Folland-Stein operator
$\mathscr{L}_\alpha$ on some examples of 3-dimensional Heisenberg Bieberbach
manifolds, that is, compact quotients $\Gamma\backslash\mathbb{H}$ of the
Heisenberg group $\mathbb{H}$ by a discrete torsion-free subgroup $\Gamma$ of
$\mathbb{H}\rtimes U(1)$.
