@article{GDZPPN00126270X, title = {The a-congruences on S(X) and the S-equivalences on X.}, journal = {Semigroup forum}, volume = {46}, year = {1993}, pages = {48-59}, zbl = {0784.20034}, url = {http://dml.mathdoc.fr/item/GDZPPN00126270X} }
Pei, H. The a-congruences on S(X) and the S-equivalences on X.. Semigroup forum, Tome 46 (1993) pp. 48-59. http://gdmltest.u-ga.fr/item/GDZPPN00126270X/