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@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/} }
J.P. Troallic; G. Hansel. Extension properties of WS-groups.. Semigroup forum, Tome 45 (1992) no. 3, pp. 63-70. http://geodesic.mathdoc.fr/item/SF_1992__45_3_135172/