Generalised knot groups distinguish the square and granny knots (with an appendix by David Savitt)
Abstract
Given a knot K we may construct a group G_n(K) from the fundamental group of K by adjoining an nth root of the meridian that commutes with the corresponding longitude. These "generalised knot groups" were introduced independently by Wada and Kelly, and contain the fundamental group as a subgroup. The square knot SK and the granny knot GK are a well known example of a pair of distinct knots with isomorphic fundamental groups. We show that G_n(SK) and G_n(GK) are non-isomorphic for all n>1. This confirms a conjecture of Lin and Nelson, and shows that the isomorphism type of G_n(K), n>1, carries more information about K than the isomorphism type of the fundamental group. An appendix by David Savitt contains some results on representations of the trefoil group in PSL(2,p) that are needed for the proof.
Keywords
Cite
@article{arxiv.0706.1807,
title = {Generalised knot groups distinguish the square and granny knots (with an appendix by David Savitt)},
author = {Christopher Tuffley},
journal= {arXiv preprint arXiv:0706.1807},
year = {2009}
}
Comments
25 pages, 5 figures, to appear in JKTR. v3: example of the target groups added; slight correction to the construction of the target groups; references updated; some changes to notation. v2: section 4.2 expanded to give overview of proof