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Preprint Number 674

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674. Martin R. Bridson and Henry Wilton
The triviality problem for profinite completions

Submission date: 10 January 2014


We prove that there is no algorithm that can determine whether or not a finitely presented group has a non-trivial finite quotient; indeed, this remains undecidable among the fundamental groups of compact, non-positively curved square complexes. We deduce that many other properties of groups are undecidable. For hyperbolic groups, there cannot exist algorithms to determine largeness, the existence of a linear representation with infinite image (over any infinite field), or the rank of the profinite completion.

Mathematics Subject Classification: 20F10, 20F67, 57M07, (20E18, 20F65)

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Full text arXiv 1401.2273: pdf, ps.

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