@article{GDZPPN001247506, title = {Perfect monoids.}, journal = {Semigroup forum}, volume = {2}, year = {1971}, pages = {95-118}, language = {en}, url = {http://dml.mathdoc.fr/item/GDZPPN001247506} }
Isbell, J.R. Perfect monoids.. Semigroup forum, Tome 2 (1971) pp. 95-118. http://gdmltest.u-ga.fr/item/GDZPPN001247506/