$\mathcal{L}$-- and $\mathcal{R}$--cross-sections in the Brauer semigoup

Abstract

We classify all cross-sections of Green's relations $\mathcal{L}$ and $\mathcal{R}$ in the Brauer semigroup. The regular behavior of such cross-sections starts from $n=7$. We show that in the regular case there are essentially two different cross-sections and all others are ${\mathcal{S}}_n$-conjugated to one of these two. We also classify all cross-sections up to isomorphism.

21 page, 5 figures