Left absorption in products of countable orders

Abstract

We classify the countable linear orders $X$ for which there is an order $A$ with at least two points such that the lexicographic product $AX$ is isomorphic to $X$. Given such an $X$, we determine every corresponding order $A$, and identify when $X$ is isomorphic to its square. More generally, we characterize the countable orders that embed at least two disjoint convex copies of themselves.