On monoids of monotone injective partial self-maps of integers with cofinite domains and images

Abstract

We study the semigroup $\mathscr{I}^{\nearrow}_{\infty}(\mathbb{Z})$ of monotone injective partial selfmaps of the set of integers having cofinite domain and image. We show that $\mathscr{I}^{\nearrow}_{\infty}(\mathbb{Z})$ is bisimple and all of its non-trivial semigroup homomorphisms are either isomorphisms or group homomorphisms. We also prove that every Baire topology $\tau$ on $\mathscr{I}^{\nearrow}_{\infty}(\mathbb{Z})$ such that $(\mathscr{I}^{\nearrow}_{\infty}(\mathbb{Z}),\tau)$ is a Hausdorff semitopological semigroup is discrete and we construct a non-discrete Hausdorff inverse semigroup topology $\tau_W$ on $\mathscr{I}^{\nearrow}_{\infty}(\mathbb{Z})$. We show that the discrete semigroup $\mathscr{I}^{\nearrow}_{\infty}(\mathbb{Z})$ cannot be embedded into some classes of compact-like topological semigroups and that its remainder under the closure in a topological semigroup $S$ is an ideal in $S$.