@article{SF_1978__16_134272,
     author = {T.E. Hall},
     title = {Inverse semigroup varieties with the amalgamation property.},
     journal = {Semigroup forum},
     pages = {37--52},
     year = {1978},
     volume = {16},
     zbl = {0396.20039},
     url = {http://geodesic.mathdoc.fr/item/SF_1978__16_134272/}
}