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@article{MZ_1970__113_171271, author = {Eric Mendelsohn}, title = {An {Elementary} {Characterization} of the {Category} of {(Free)} {Relational} {Systems.}}, journal = {Mathematische Zeitschrift}, pages = {224--232}, publisher = {mathdoc}, volume = {113}, year = {1970}, zbl = {0206.30001}, url = {http://geodesic.mathdoc.fr/item/MZ_1970__113_171271/} }
Eric Mendelsohn. An Elementary Characterization of the Category of (Free) Relational Systems.. Mathematische Zeitschrift, Tome 113 (1970), pp. 224-232. http://geodesic.mathdoc.fr/item/MZ_1970__113_171271/