Folding of set-theoretical solutions of the Yang-Baxter equation

We establish a correspondence between the invariant subsets of a non-degenerate symmetric set-theoretical solution of the quantum Yang-Baxter equation and the parabolic subgroups of its structure group, equipped with its canonical Garside structure. Moreover, we introduce the notion of a foldable solution, which extends the one of a decomposable solution

A note on Garside monoids and Braces

A left brace is a triple $(\mathcal{B},+,\cdot)$, where $(\mathcal{B},+)$ is an abelian group, $(\mathcal{B},\cdot)$ is a group, and there is a left-distributivity-like axiom that relates between the two operations in $\mathcal{B}$. In analogy with a left brace, we define a left $\mathscr{M}$-brace to be a triple $(\mathcal{B},+,\cdot)$, where $(\mathcal{B},+)$ is a commutative monoid, $(\mathcal{B},\cdot)$ is a monoid, and the axiom of left distributivity holds. A lcm-monoid $M$ is a left-cancellative monoid such that $1$ is the unique invertible element in $M$, and every pair of elements in $M$ admit a lcm with respect to left-divisibility. The class of lcm-monoids contains the Gaussian, quasi-Garside and Garside monoids. We show that every lcm-monoid induces a left $\mathscr{M}$-brace. Furthermore, we show that every Gaussian group induces a partial left brace.Comment: 12 pages, 5 figure