Scaled Heisenberg lattice ($N_k=\{(x,y,z):x,y,z\in k\mathbb{Z}\}$)

In the real Heisenberg group with multiplication $(x,y,z)(x^{\prime },y^{\prime },z^{\prime })=(x+x^{\prime },y+y^{\prime },z+z^{\prime }+x{y}^{\prime })$, the displayed set is a discrete cocompact subgroup. Writing $a=(k,0,0)$, $b=(0,k,0)$, $c=(0,0,k)$ gives $[a,b]=c^k$ and $c$ central. Hence its abelianization is ${\mathbb{Z}}^2\oplus \mathbb{Z}/k$. The right quotient maps to ${\mathbb{R}}^2/k{\mathbb{Z}}^2$ by its first two coordinates; each fibre is the central circle $\mathbb{R}/k\mathbb{Z}$.