Abstract
A generalised D-semigroup is here defined to be a left E-semiabundant semigroup S in which the \(\overline{\mathcal R}_E\)-class of every \(x\in S\) contains a unique element D(x) of E, made into a unary semigroup. Two-sided versions are defined in the obvious way in terms of \(\overline{\mathcal R}_E\) and \(\overline{\mathcal L}_E\). The resulting class of unary (bi-unary) semigroups is shown to be a finitely based variety, properly containing the variety of D-semigroups (defined in an order-theoretic way in Communications in Algebra, 3979–4007, 2014). Important subclasses associated with the regularity and abundance properties are considered. The full transformation semigroup \(T_X\) can be made into a generalised D-semigroup in many natural ways, and an embedding theorem is given. A generalisation of inverse semigroups in which inverses are defined relative to a set of idempotents arises as a special case, and a finite equational axiomatisation of the resulting unary semigroups is given.
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Acknowledgements
The author acknowledges the assistance of the automated deduction tools Prover9 and Mace4, both developed by McCune [15]. Examples 2.16 and 3.9 were both obtained with the aid of Mace4, and the proof that generalised D-semigroups form a variety was obtained with the assistance of Prover9. The author also acknowledges the very helpful comments and suggestions of the referee.
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Communicated by Victoria Gould.
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Stokes, T. Generalised domain and E-inverse semigroups. Semigroup Forum 97, 32–52 (2018). https://doi.org/10.1007/s00233-018-9917-6
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DOI: https://doi.org/10.1007/s00233-018-9917-6