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@article{PORMA_1975__34_3_115261, author = {Rosenberg, I.G.}, title = {Special types of universal algebras preserving a relation}, journal = {Portugaliae mathematica}, pages = {173--188}, publisher = {mathdoc}, volume = {34}, number = {3}, year = {1975}, mrnumber = {0465992}, zbl = {0327.08008}, language = {en}, url = {http://geodesic.mathdoc.fr/item/PORMA_1975__34_3_115261/} }
Rosenberg, I.G. Special types of universal algebras preserving a relation. Portugaliae mathematica, Tome 34 (1975) no. 3, pp. 173-188. http://geodesic.mathdoc.fr/item/PORMA_1975__34_3_115261/