Palindromic width of graph of groups


In this paper, we answer questions raised by Bardakov and Gongopadhyay (Commun. Algebra 43(11) (2015) 4809–4824). We prove that the palindromic width of HNN extension of a group by proper associated subgroups is infinite. We also prove that the palindromic width of the amalgamated free product of two groups via a proper subgroup is infinite (except when the amalgamated subgroup has index two in each of the factors). Combining these results it follows that the palindromic width of the fundamental group of a graph of groups is mostly infinite.

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The first author (KG) acknowledges partial support from the Grant DST/INT/RUS/RSF/P-19.

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Correspondence to Krishnendu Gongopadhyay.

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Communicating Editor: B Sury

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Gongopadhyay, K., Krishna, S. Palindromic width of graph of groups. Proc Math Sci 130, 22 (2020).

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  • Palindromic width
  • graph of groups
  • HNN extension
  • amalgamated free product

2010 Mathematics Subject Classification

  • Primary: 20F65
  • Secondary: 20E06