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@article{MS2_1962__11_165827, author = {Bjarni Jonsson}, title = {Algebraic {Extensions} of {Relational} {Systems.}}, journal = {Mathematica Scandinavica}, pages = {179--205}, publisher = {mathdoc}, volume = {11}, year = {1962}, zbl = {0201.34403}, url = {http://geodesic.mathdoc.fr/item/MS2_1962__11_165827/} }
Bjarni Jonsson. Algebraic Extensions of Relational Systems.. Mathematica Scandinavica, Tome 11 (1962), pp. 179-205. http://geodesic.mathdoc.fr/item/MS2_1962__11_165827/