@article{GDZPPN00125166X, title = {Semilattices of width 2.}, journal = {Semigroup forum}, volume = {12}, year = {1976}, pages = {149-177}, zbl = {0354.06001}, url = {http://dml.mathdoc.fr/item/GDZPPN00125166X} }
Sirjaev, V.M. Semilattices of width 2.. Semigroup forum, Tome 12 (1976) pp. 149-177. http://gdmltest.u-ga.fr/item/GDZPPN00125166X/