@article{SLC_1987_16_a7,
     author = {Giuseppe Pirillo},
     title = {On {\ensuremath{\omega}-Ramseyan} {Semigroups}},
     journal = {S\'eminaire lotharingien de combinatoire},
     year = {1987},
     volume = {16},
     url = {http://geodesic.mathdoc.fr/item/SLC_1987_16_a7/}
}