@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/}
}