In this article we consider transient random walks on HNN extensions of finitely generated groups. We prove that the rate escape w.r.t. some generalised word length exists. Moreover, a central limit theorem with respect to is derived. Finally, show escape, which can be regarded as function in many parameters describe walk, behaves real-analytic terms probability measures constant support.

We prove that the amalgamated product of free groups with cyclic amalgamations satisfying certain conditions are virtually free-by-cyclic. In case the cyclic amalgamated subgroups lie outside the derived group such groups are free-by-cyclic. Similarly a one-relator HNN-extension in which the conjugated elements either coincide or are independent modulo the derived group is shown to be free-by-c...

By estimating the subgroup numbers associated with various classes of large groups, we exhibit a number of new phenomena in the theory of subgroup growth. Key-words: subgroup growth, large groups, one-relator groups, HNN-extensions MSC-Index: 20E07

We discuss embedding theorems for HNN extensions and clarify the relationship between the concept by Gilbert and that of Yamamura. We employ the automata theoretical technique based on the combinatorial and geometrical properties of Schützenberger graphs.