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@article{SF_1994__49_2_135336, author = {D.V. Dekov}, title = {HNN extensions of semigroups.}, journal = {Semigroup forum}, pages = {83--88}, publisher = {mathdoc}, volume = {49}, number = {2}, year = {1994}, zbl = {0803.20039}, url = {http://geodesic.mathdoc.fr/item/SF_1994__49_2_135336/} }
D.V. Dekov. HNN extensions of semigroups.. Semigroup forum, Tome 49 (1994) no. 2, pp. 83-88. http://geodesic.mathdoc.fr/item/SF_1994__49_2_135336/