@article{SF_1976__13_134219,
     author = {T.S. Blyth},
     title = {On middle units in orthodox semigroups.},
     journal = {Semigroup forum},
     pages = {261--266},
     publisher = {mathdoc},
     volume = {13},
     year = {1976},
     zbl = {0353.20057},
     url = {http://geodesic.mathdoc.fr/item/SF_1976__13_134219/}
}