@article{GDZPPN001255622, title = {Graph Monoids.}, journal = {Semigroup forum}, volume = {24}, year = {1982}, pages = {1-8}, zbl = {0497.05060}, url = {http://dml.mathdoc.fr/item/GDZPPN001255622} }
Roush, F.W.; Kim, K.H.; Makar-Limanov, L.G. Graph Monoids.. Semigroup forum, Tome 24 (1982) pp. 1-8. http://gdmltest.u-ga.fr/item/GDZPPN001255622/