Exponentiable linear orders need not be transitive

TL;DR

The paper demonstrates that not all exponentiable linear orders are transitive by introducing cyclically transitive linear orders and showing some are exponentiable, thus answering a longstanding question.

Contribution

It defines the class CTLO of cyclically transitive linear orders and proves that all discrete unbounded orders in CTLO are exponentiable, providing a negative answer to the transitivity question.

Findings

Discrete unbounded orders in CTLO are exponentiable.

Not all exponentiable linear orders are transitive.

The class CTLO relates to cyclic orders by Droste, Giraudet, and Macpherson.

Abstract

It is well-known that every transitive linear order is exponentiable. However, is the converse true? This question was posed in Chapter 8 of the textbook titled "Linear Orderings" by Rosenstein. We define the class CTLO of cyclically transitive linear orders that properly contains the class of transitive linear orders, and show that all discrete unbounded orders in CTLO are exponentiable, thereby providing a negative answer to the question. The class CTLO is closely related to the class of transitive cyclic orders introduced by Droste, Giraudet and Macpherson. We also discuss the closure of subclasses of CTLO under products and iterated Hausdorff condensations.