@article{SLC_1987_16_a8,
     author = {Giuseppe Pirillo},
     title = {Su alcune propriet\`a del semigruppi finiti},
     journal = {S\'eminaire lotharingien de combinatoire},
     publisher = {mathdoc},
     volume = {16},
     year = {1987},
     url = {http://geodesic.mathdoc.fr/item/SLC_1987_16_a8/}
}