@article{SF_1975__10_134118,
     author = {A.H. Clifford},
     title = {The partial groupoid of idempotents of a regular semigroup.},
     journal = {Semigroup forum},
     pages = {262--268},
     publisher = {mathdoc},
     volume = {10},
     year = {1975},
     zbl = {0299.20045},
     url = {http://geodesic.mathdoc.fr/item/SF_1975__10_134118/}
}