On the algebraic and arithmetic structure of the monoid of product-one sequences

Let $G$ be a finite group. A finite unordered sequence $S = g_1 \boldsymbol{\cdot} \ldots \boldsymbol{\cdot} g_{\ell}$oftermsfrom$G$, where repetition is allowed, is a product-one sequence if its terms can be ordered such that their product equals $1_G$, the identity element of the group. As usual, we consider sequences as elements of the free abelian monoid $\mathcal F (G)$withbasis$G$,andwestudythesubmonoid$\mathcal B (G) \subset \mathcal F (G)$ of all product-one sequences. This is a finitely generated C-monoid, which is a Krull monoid if and only if $G$ is abelian. In case of abelian groups, $\mathcal{B}(G)$ is a well-studied object. In the present paper we focus on non-abelian groups, and we study the class semigroup and the arithmetic of $\mathcal{B}(G)$.