@article{SF_1976__12_134173,
     author = {A. B. Engel},
     title = {Necessary conditions for a semigroup to be an integral {CRM-ring} with identity.},
     journal = {Semigroup forum},
     pages = {207--214},
     publisher = {mathdoc},
     volume = {12},
     year = {1976},
     zbl = {0328.20061},
     url = {http://geodesic.mathdoc.fr/item/SF_1976__12_134173/}
}