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@article{SF_1971__3_133847, author = {K.K.H. Butler}, title = {On (0,1)-matrix semigroups.}, journal = {Semigroup forum}, pages = {74--79}, publisher = {mathdoc}, volume = {3}, year = {1971}, zbl = {0228.20059}, url = {http://geodesic.mathdoc.fr/item/SF_1971__3_133847/} }
K.K.H. Butler. On (0,1)-matrix semigroups.. Semigroup forum, Tome 3 (1971), pp. 74-79. http://geodesic.mathdoc.fr/item/SF_1971__3_133847/