@article{SF_1975__10_134096,
     author = {T.E. Hays},
     title = {Irreducible semigroups are monotone.},
     journal = {Semigroup forum},
     pages = {25--31},
     publisher = {mathdoc},
     volume = {10},
     year = {1975},
     zbl = {0298.22002},
     url = {http://geodesic.mathdoc.fr/item/SF_1975__10_134096/}
}