# On the semigroup $\textbf{ID}_{\infty}$

## TL;DR

This paper investigates the algebraic structure and topological properties of the semigroup of all partial isometries of integers, revealing its isomorphism to a semidirect product and exploring conditions for various topologies.

## Contribution

It characterizes the semigroup $ extbf{ID}_{
abla}$, establishes its isomorphism to a semidirect product, and analyzes topological conditions for $ extbf{ID}_{
abla}$.

## Key findings

- $ extbf{ID}_{
abla}$ is an $F$-inverse semigroup.
- The quotient $ extbf{ID}_{
abla}/ extsf{C}_{ ext{mg}}$ is isomorphic to ${ extsf{Iso}}(
abla)$.
- Conditions for discrete and non-discrete Hausdorff topologies are provided.

## Abstract

We study the semigroup $\textbf{{ID}}_{\infty}$ of all partial isometries of the set of integers $\mathbb{Z}$. It is proved that the quotient semigroup $\textbf{{ID}}_{\infty}/\mathfrak{C}_{\textsf{mg}}$, where $\mathfrak{C}_{\textsf{mg}}$ is the minimum group congruence, is isomorphic to the group ${\textsf{Iso}}(\mathbb{Z})$ of all isometries of $\mathbb{Z}$, $\textbf{{ID}}_{\infty}$ is an $F$-inverse semigroup, and $\textbf{{ID}}_{\infty}$ is isomorphic to the semidirect product ${\textsf{Iso}}(\mathbb{Z})\ltimes_\mathfrak{h}\mathscr{P}_{\!\infty}(\mathbb{Z})$ of the free semilattice with unit $(\mathscr{P}_{\!\infty}(\mathbb{Z}),\cup)$ by the group ${\textsf{Iso}}(\mathbb{Z})$. We give the sufficient conditions on a shift-continuous topology $\tau$ on $\textbf{{ID}}_{\infty}$ when $\tau$ is discrete. A non-discrete Hausdorff semigroup topology on $\textbf{{ID}}_{\infty}$ is constructed. Also, the problem of an embedding of the discrete semigroup $\textbf{{ID}}_{\infty}$ into Hausdorff compact-like topological semigroups is studied.