@article{SF_1983__26_134601,
     author = {P.G. Trotter},
     title = {Projectives in inverse semigroups.},
     journal = {Semigroup forum},
     pages = {167--190},
     publisher = {mathdoc},
     volume = {26},
     year = {1983},
     zbl = {0509.20045},
     url = {http://geodesic.mathdoc.fr/item/SF_1983__26_134601/}
}