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Published online by Cambridge University Press: 23 December 2024
The group of order-preserving automorphisms of a finitely generated Archimedean ordered group of rank $2$ is either infinite cyclic or trivial according as the ratio in
$\mathbb {R}$ of the generators of the subgroup is or is not quadratic over
$\mathbb {Q}.$ In the case of an Archimedean ordered group of rank
$2$ that is not finitely generated, the group of order-preserving automorphisms is free abelian. Criteria determining the rank of this free abelian group are established.