@article{SF_1976__13_134194,
     author = {D.W. Hardy and Y. Tirasupa},
     title = {Semilattices of proper inverse semigroups.},
     journal = {Semigroup forum},
     pages = {29--36},
     publisher = {mathdoc},
     volume = {13},
     year = {1976},
     zbl = {0337.20027},
     url = {http://geodesic.mathdoc.fr/item/SF_1976__13_134194/}
}