@article{SF_1976__13_134223,
     author = {V.A. Fortunatov},
     title = {Congruences on simple extensions of semigroups.},
     journal = {Semigroup forum},
     pages = {283--296},
     year = {1976},
     volume = {13},
     zbl = {0354.20049},
     url = {http://geodesic.mathdoc.fr/item/SF_1976__13_134223/}
}