Abstract
The theory of group actions on trees is used to produce a proof of Grushko’s theorem, which extends to a theorem involving amalgamated free products; this mimics the author’s topological proof, but some new consequences are drawn. Theorems of Shenitzer and Swarup on amalgamations and HNN-extensions over cyclic subgroups are deduced as a consequence and somewhat generalized.
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© 1991 Springer-Verlag New York, Inc.
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Stallings, J.R. (1991). Foldings of G-trees. In: Alperin, R.C. (eds) Arboreal Group Theory. Mathematical Sciences Research Institute Publications, vol 19. Springer, New York, NY. https://doi.org/10.1007/978-1-4612-3142-4_14
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DOI: https://doi.org/10.1007/978-1-4612-3142-4_14
Publisher Name: Springer, New York, NY
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