M\"obius function of semigroup posets through Hilbert series
  In this paper, we investigate the M{\"o}bius function $\mu\_{\mathcal{S}}$ associated to a (locally finite) poset arising from a semigroup $\mathcal{S}$ of $\mathbb{Z}^m$. We introduce and develop a new approach to study $\mu\_{\mathcal{S}}$ by using the Hilbert series of $\mathcal{S}$. The latter enables us to provide formulas for $\mu\_{\mathcal{S}}$ when $\mathcal{S}$ belongs to certain families of semigroups. Finally, a characterization for a locally finite poset to be isomorphic to a semigroup poset is given. 
Jonathan Chappelon (IMAG), Ignacio Garc\'ia-Marco (IMAG), Luis Pedro   Montejano (IMAG), Jorge Luis Ram\'irez Alfons\'in (IMAG)
math.GR math.CO math.NT