An Improved Subgroup Theorem for HNN Groups with Some Applications
- 1 February 1974
- journal article
- Published by Canadian Mathematical Society in Canadian Journal of Mathematics
- Vol. 26 (1) , 214-224
- https://doi.org/10.4153/cjm-1974-021-1
Abstract
In [4], a subgroup theorem for HNN groups was established. The theorem was proved by embedding the given HNN group in a free product with amalgamated subgroup and then applying the subgroup theorem of [3]. In this paper we obtain a sharper form of the subgroup theorem of [4] by applying the Reidemeister-Schreier method directly, using an appropriate Schreier system of coset representatives. Specifically, we prove (in Theorem 1) that if H is a subgroup of the HNN group 1Keywords
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