@article{SF_1971__2_133819,
     author = {J.R. Isbell},
     title = {Perfect monoids.},
     journal = {Semigroup forum},
     pages = {95--118},
     year = {1971},
     volume = {2},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SF_1971__2_133819/}
}