@article{10_1017_S0017089500031840,
     author = {Billhardt, Bernd},
     title = {Extensions of semilattices by left {type-A} semigroups},
     journal = {Glasgow mathematical journal},
     pages = {7--16},
     year = {1997},
     volume = {39},
     number = {1},
     doi = {10.1017/S0017089500031840},
     url = {http://geodesic.mathdoc.fr/articles/10.1017/S0017089500031840/}
}