Left Absorption in Products of Countable Orders
摘要
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.