On locally compact shift-continuous topologies on the $\alpha$-bicyclic monoid

Abstract

A topology $\tau$ on a monoid $S$ is called {\em shift-continuous} if for every $a,b\in S$ the two-sided shift $S\to S$, $x\mapsto axb$, is continuous. For every ordinal $\alpha\le \omega$, we describe all shift-continuous locally compact Hausdorff topologies on the $\alpha$-bicyclic monoid $\mathcal{B}_{\alpha}$. More precisely, we prove that the lattice of shift-continuous locally compact Hausdorff topologies on $\mathcal{B}_{\alpha}$ is anti-isomorphic to the segment of $[1,\alpha]$ of ordinals, endowed with the natural well-order. Also we prove that for each ordinal $\alpha$ the $\alpha+1$-bicyclic monoid $\mathcal{B}_{\alpha+1}$ is isomorphic to the Bruck extension of the $\alpha$-bicyclic monoid $\mathcal{B}_{\alpha}$.