@article{SF_1972__5_133930,
     author = {A.H. Clifford},
     title = {The structure of bisimple left unipotent semigroups as ordered pairs.},
     journal = {Semigroup forum},
     pages = {137--144},
     publisher = {mathdoc},
     volume = {5},
     year = {1972},
     zbl = {0264.20045},
     url = {http://geodesic.mathdoc.fr/item/SF_1972__5_133930/}
}