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Formations of orthodox semigroups

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Abstract

Taking formations of groups and of inverse semigroups as the starting point, formations of orthodox semigroups are defined, as well as the wider class of i-formations (i standing for idempotent-separating). The relation between the nature of a class of inverse semigroups \(\mathscr {F}\) [of groups \(\mathscr {G}\)] and that of certain classes of orthodox semigroups with associated inverse semigroups in \(\mathscr {F}\) [groups in \(\mathscr {G}\)] is discussed. The product of formations of orthodox semigroups, in particular of R-unipotent semigroups, is considered, and a product like the Gaschütz product known for groups is presented for i-formations. The paper concludes with a list of questions.

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Acknowledgements

This work was developed within the activities of Centro de Matemática Computacional e Estocástica, CEMAT, and Departamento de Matemática da Faculdade de Ciências da Universidade de Lisboa, within the projects UIDB/04621/2020 and UIDP/04621/2020, financed by Fundação para a Ciência e a Tecnologia, FCT. The authors would like to thank Adolfo Ballester-Bolinches and Mikhail Volkov for providing some of the references, Luís Sequeira for computing various examples and Mário J.J. Branco for some interesting discussions.

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Correspondence to Gracinda M. S. Gomes.

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Communicated by Victoria Gould.

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Gomes, G.M.S., Monteiro, AC.C. Formations of orthodox semigroups. Semigroup Forum 107, 651–679 (2023). https://doi.org/10.1007/s00233-023-10390-x

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