@article{SF_1974__9_134062,
     author = {F.R. McMorris and C.S. Johnson},
     title = {Retractions and {S-endomorphisms.}},
     journal = {Semigroup forum},
     pages = {84--87},
     publisher = {mathdoc},
     volume = {9},
     year = {1974},
     zbl = {0299.20054},
     url = {http://geodesic.mathdoc.fr/item/SF_1974__9_134062/}
}