It is shown that the compressed word problem for an HNNextension 〈H, t | tat = φ(a)(a ∈ A)〉 with A finite is polynomial time Turing-reducible to the compressed word problem for the base group H . An analogous result for amalgamated free products is shown as well.

In this paper we study residual solvability of the amalgamated product of two finitely generated free groups, in the case of doubles. We find conditions where this kind of structure is residually solvable, and show that in general this is not the case. However this kind of structure is always meta-residually-solvable.

In this paper we propose a method to construct logarithmic signatures which are not amalgamated transversal and further do not even have a periodic block. The latter property was crucial for the successful attack on the system MST 3 by Blackburn et al. [1]. The idea for our construction is based on the theory in Szabó’s book about group factorizations [12].