Acta Mathematica Hungarica

, Volume 157, Issue 1, pp 80–120

# Inductive groupoids and cross-connections of regular semigroups

• P. A. Azeef Muhammed
• M. V. Volkov
Article

## Abstract

There are two major structure theorems for an arbitrary regular semigroup using categories, both due to Nambooripad. The first construction using inductive groupoids departs from the biordered set structure of a given regular semigroup. This approach belongs to the realm of the celebrated Ehresmann–Schein–Nambooripad Theorem and its subsequent generalisations. The second construction is a generalisation of Grillet’s work on cross-connected partially ordered sets, arising from the principal ideals of the given semigroup. In this article, we establish a direct equivalence between these two seemingly different constructions. We show how the cross-connection representation of a regular semigroup may be constructed directly from the inductive groupoid of the semigroup, and vice versa.

## Key words and phrases

regular semigroup biordered set inductive groupoid crossconnection normal category

## Mathematics Subject Classification

20M10 20M17 20M50 18B40 06A75

## Notes

### Acknowledgements

We are very grateful to J. Meakin, University of Nebraska-Lincoln, for reading an initial draft of the article and helping us with several enlightening suggestions. We also thank the referee for the careful reading of the article and the detailed comments which helped us to improve the manuscript.

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