@article{SF_1977__14_186358,
     author = {J. B. Fountain and P. Lockley},
     title = {Semilattices of groups with distributive congruence lattice.},
     journal = {Semigroup forum},
     pages = {81--92},
     publisher = {mathdoc},
     volume = {14},
     year = {1977},
     zbl = {0392.20041},
     url = {http://geodesic.mathdoc.fr/item/SF_1977__14_186358/}
}