c-Regular cyclically ordered groups

We define and we characterize regular and c-regular cyclically ordered abelian groups. We prove that every dense c-regular cyclically ordered abelian group is elementarily equivalent to some cyclically ordered group of unimodular complex numbers, that every discrete c-regular cyclically ordered abelian group is elementarily equivalent to some ultraproduct of finite cyclic groups, and that the discrete regular non-c-regular cyclically ordered abelian groups are elementarily equivalent to the linearly cyclically ordered group of integers.Comment: 20 page

Infinite words and universal free actions

This is the second paper in a series of three, where we take on the unified theory of non-Archimedean group actions, length functions and infinite words. Here, for an arbitrary group $G$ of infinite words over an ordered abelian group $\Lambda$ we construct a $\Lambda$-tree $\Gamma_G$ equipped with a free action of $G$. Moreover, we show that $\Gamma_G$ is a universal tree for $G$ in the sense that it isometrically embeds in every $\Lambda$-tree equipped with a free $G$-action compatible with the original length function on $G$.Comment: 20 pages, 4 figure

ZnZ^n-free groups are CAT(0)

We show that every group with free $\mathbb{Z}^n$-length function is CAT(0).Comment: To be published in the Journal of the London Mathematical Society. This version is very close to the accepted version. The exposition greatly improved due to the referee's comment