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Congruences on orthodox semigroups with associate subgroups

Published online by Cambridge University Press:  18 May 2009

T. S. Blyth
Affiliation:
Mathematical Institute, University of St Andrews, Scotland
Emília Giraldes
Affiliation:
Departamento de Matemática, F.C.T., Universidade Nova de Lisboa, Portugal
M. Paula O. Marques-Smith
Affiliation:
Departamento de Matemática, Universidade do Minho, Portugal
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If Sis a regular semigroup then an inverse transversal of S is an inverse subsemigroup T with the property that |T ∩ V(x)| = 1 for every xS where V(x) denotes the set of inverses of x ∈ S. In a previous publication [1] we considered the similar concept of a subsemigroup T of S such that |TA(x)| = 1 for every xS where A(x) = {yS;xyx = x} denotes the set of associates (or pre-inverses) of xS, and showed that such a subsemigroup T is necessarily a maximal subgroup Ha for some idempotent α ∈ S. Throughout what follows, we shall assume that S is orthodox and α is a middle unit (in the sense that xαy = xy for all x, y ∈ S). Under these assumptions, we obtained in [1] a structure theorem which generalises that given in [3] for uniquely unit orthodox semigroups. Adopting the notation of [1], we let T ∩ A(x) = {x*} and write the subgroup T as Hα = {x*;xS}, which we call an associate subgroup of S. For every xS we therefore have x*α = x* = αx* and x*x** = α = x**x*. As shown in [1, Theorems 4, 5] we also have (xy)* = y*x* for all x, yS, and e* = α for every idempotent e.

Type
Research Article
Copyright
Copyright © Glasgow Mathematical Journal Trust 1996

References

REFERENCES

1.Blyth, T. S., Giraldes, Emilia and Marques-Smith, M. Paula O., Associate subgroups of orthodox semigroups, Glasgow Math. J. 36 (1994), 163171.Google Scholar
2.Blyth, T. S. and Janowitz, M. F., Residuation theory (Pergamon Press, 1972).Google Scholar
3.Blyth, T. S. and McFadden, R., Unit orthodox semigroups, Glasgow Math. J. 24 (1983), 3942.CrossRefGoogle Scholar