@article{1102976437, author = {Kahn, Harold David}, title = {Covering semigroups.}, journal = {Pacific J. Math.}, volume = {35}, number = {3}, year = {1970}, pages = { 427-439}, language = {en}, url = {http://dml.mathdoc.fr/item/1102976437} }
Kahn, Harold David. Covering semigroups.. Pacific J. Math., Tome 35 (1970) no. 3, pp. 427-439. http://gdmltest.u-ga.fr/item/1102976437/