Isbell's subfactor projections in a noetherian form
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arXiv
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| Format: | Preprint |
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2024
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| _version_ | 1866915260550610944 |
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| author | Dayaram, Kishan Goswami, Amartya Janelidze, Zurab |
| author_facet | Dayaram, Kishan Goswami, Amartya Janelidze, Zurab |
| contents | In this paper, we revisit the 1979 work of Isbell on subfactors of groups and their projections, which he uses to establish a stronger formulation of the butterfly lemma and its consequence, the refinement theorem for subnormal series of subgroups. We point out an error in the second part of Isbell's refinement theorem, but show that the rest of his results can be extended to the general self-dual context of a noetherian form, which includes in its scope all semi-abelian categories as well as all Grandis exact categories. Furthermore, we show that Isbell's formulations of the butterfly lemma and the refinement theorem amount to canonicity of isomorphisms established in these results. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2408_05731 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Isbell's subfactor projections in a noetherian form Dayaram, Kishan Goswami, Amartya Janelidze, Zurab Group Theory 18D30, 20J15, 18E13, 20E15, 06A15 In this paper, we revisit the 1979 work of Isbell on subfactors of groups and their projections, which he uses to establish a stronger formulation of the butterfly lemma and its consequence, the refinement theorem for subnormal series of subgroups. We point out an error in the second part of Isbell's refinement theorem, but show that the rest of his results can be extended to the general self-dual context of a noetherian form, which includes in its scope all semi-abelian categories as well as all Grandis exact categories. Furthermore, we show that Isbell's formulations of the butterfly lemma and the refinement theorem amount to canonicity of isomorphisms established in these results. |
| title | Isbell's subfactor projections in a noetherian form |
| topic | Group Theory 18D30, 20J15, 18E13, 20E15, 06A15 |
| url | https://arxiv.org/abs/2408.05731 |