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Abstract: Groups acting freely on -trees (-free groups) play a key role in the study of non-archimedean group actions. Following Stallingsʼ ideas, we develop graph-theoretic techniques to investigate subgroup structure of -free groups. As an immediate application of the presented method, we give an effective solution to the Uniform Membership Problem and the Power Problem in -free groups. [Copyright &y& Elsevier]

This is the first paper in a series of three where we take on the unified theory of non-Archimedean group actions, length functions and infinite words. Our main goal is to show that group actions on Zn-trees give one a powerful tool to study groups. All finitely generated groups acting freely on R-trees also act freely on some Zn-trees, but the latter ones form a much larger class. The natural effectiveness of all constructions for Zn-actions (which is not the case for R-trees) comes along with a robust algorithmic theory. In this paper we describe the algebraic structure of finitely generated groups acting freely and regularly on Zn-trees and give necessary and sufficient conditions for such actions. [ABSTRACT FROM AUTHOR]

In this paper we discuss a general approach to positive theories of groups. As an application we get a robust description of positive theories of groups with regular free Lyndon length function. Our approach combines techniques of infinite words (see [17, 3]), cancellation diagrams introduced in [14], and Merzlyakov's method [15]. [ABSTRACT FROM AUTHOR]

This is the first paper in a series of three where we take on the unified theory of non-Archimedean group actions, length functions and infinite words. Our main goal is to show that group actions on Zn-trees give one a powerful tool to study groups. All finitely generated groups acting freely on R-trees also act freely on some Zn-trees, but the latter ones form a much larger class. The natural effectiveness of all constructions for Zn-actions (which is not the case for R-trees) comes along with a robust algorithmic theory. In this paper we describe the algebraic structure of finitely generated groups acting freely and regularly on Zn-trees and give necessary and sufficient conditions for such actions. [ABSTRACT FROM AUTHOR]