@article{10_1017_S0017089500003785,
     author = {Petrich, Mario},
     title = {Congruences on simple \ensuremath{\omega}-semigroups},
     journal = {Glasgow mathematical journal},
     pages = {87--101},
     year = {1979},
     volume = {20},
     number = {2},
     doi = {10.1017/S0017089500003785},
     url = {http://geodesic.mathdoc.fr/articles/10.1017/S0017089500003785/}
}