@article{SF_1992__45_3_135172,
     author = {J.P. Troallic and G. Hansel},
     title = {Extension properties  of {WS-groups.}},
     journal = {Semigroup forum},
     pages = {63--70},
     publisher = {mathdoc},
     volume = {45},
     number = {3},
     year = {1992},
     zbl = {0774.43005},
     url = {http://geodesic.mathdoc.fr/item/SF_1992__45_3_135172/}
}