@article{GDZPPN00126379X, title = {A concept of variety for regular biordered sets.}, journal = {Semigroup forum}, volume = {48}, year = {1994}, pages = {335-348}, zbl = {0814.20041}, url = {http://dml.mathdoc.fr/item/GDZPPN00126379X} }
Broeksteeg, R. A concept of variety for regular biordered sets.. Semigroup forum, Tome 48 (1994) pp. 335-348. http://gdmltest.u-ga.fr/item/GDZPPN00126379X/