@article{SF_1994__48_3_135313,
     author = {K. Denecke and S.L. Wismath},
     title = {Solid varieties of semigroups.},
     journal = {Semigroup forum},
     pages = {219--234},
     year = {1994},
     volume = {48},
     number = {3},
     zbl = {0797.20045},
     url = {http://geodesic.mathdoc.fr/item/SF_1994__48_3_135313/}
}