@article{SF_1978__16_134283,
     author = {W.R. Nico},
     title = {The core congruence on a monoid.},
     journal = {Semigroup forum},
     pages = {141--146},
     publisher = {mathdoc},
     volume = {16},
     year = {1978},
     zbl = {0389.20055},
     url = {http://geodesic.mathdoc.fr/item/SF_1978__16_134283/}
}