Papers › Discrete and free groups acting on locally finite trees

Discrete and free groups acting on locally finite trees

21 Oct 2021arXiv:2110.10904links table onlyarchive 2025-07-28

Matthew J. Conder

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We present an algorithm to decide whether or not a finitely generated subgroup of the isometry group of a locally finite simplicial tree is both discrete and free. The correctness of this algorithm relies on the following conjecture: every `minimal' n-tuple of isometries of a simplicial tree either contains an elliptic element or satisfies the hypotheses of the Ping Pong Lemma. We prove this conjecture for n=2,3, and show that it implies a generalisation of Ihara's Theorem.

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