Topological finiteness properties of monoids Part 2: special monoids, one-relator monoids, amalgamated free products, and HNN extensions

Gray, Robert D. and Steinberg, Benjamin (2024) Topological finiteness properties of monoids Part 2: special monoids, one-relator monoids, amalgamated free products, and HNN extensions. Documenta Mathematica, 29 (3). pp. 511-560. ISSN 1431-0643

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Abstract

We show how topological methods developed in a previous article can be applied to prove new results about topological and homological finiteness properties of monoids. A monoid presentation is called special if the right-hand side of each relation is equal to 1. We prove results which relate the finiteness properties of a monoid defined by a special presentation with those of its group of units. Specifically we show that the monoid inherits the finiteness properties F n and FP n from its group of units. We also obtain results which relate the geometric and cohomological dimensions of such a monoid to those of its group of units. We apply these results to prove a Lyndon’s Identity Theorem for one-relator monoids of the form (Formula Presented). In particular, we show that all such monoids are of type F ∞ (and FP ∞), and that when r is not a proper power, then the monoid has geometric and cohomological dimension at most 2. The first of these results, resolves an important case of a question of Kobayashi from 2000 on homological finiteness properties of one-relator monoids. We also show how our topological approach can be used to prove results about the closure properties of various homological and topological finiteness properties for amalgamated free products and HNN-extensions of monoids. To prove these results we introduce new methods for constructing equivariant classifying spaces for monoids, as well as developing a Bass–Serre theory for free constructions of monoids.

Item Type: Article
Additional Information: Funding. This work was supported by the EPSRC grants EP/N033353/1 “Special inverse monoids: subgroups, structure, geometry, rewriting systems and the word problem” and EP/V032003/1 “Algorithmic, topological and geometric aspects of infinite groups, monoids and inverse semigroups”. The second author was supported by NSA MSP #H98230-16-1-0047 and a PSC-CUNY award.
Uncontrolled Keywords: bass–serre tree,hnn extension,hochschild cohomological dimension,classifying space,cohomological dimension,equivariant cw-complex,free product with amalgamation,geometric dimension,homological finiteness property,monoid,one-relator monoid,special monoid,mathematics(all) ,/dk/atira/pure/subjectarea/asjc/2600
Faculty \ School: Faculty of Science > School of Mathematics
UEA Research Groups: Faculty of Science > Research Groups > Logic
Faculty of Science > Research Groups > Algebra and Combinatorics
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Depositing User: LivePure Connector
Date Deposited: 25 Mar 2024 13:31
Last Modified: 03 Jun 2024 08:31
URI: https://ueaeprints.uea.ac.uk/id/eprint/94746
DOI: 10.4171/DM/959

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