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@article{ARM_1989__25_1-2_a4, author = {Gr\"atzer, G. and Wenzel, G. H.}, title = {Tolerances, covering systems, and the axiom of choice}, journal = {Archivum mathematicum}, pages = {27--34}, publisher = {mathdoc}, volume = {25}, number = {1-2}, year = {1989}, mrnumber = {1189196}, zbl = {0711.08002}, language = {en}, url = {http://geodesic.mathdoc.fr/item/ARM_1989__25_1-2_a4/} }
Grätzer, G.; Wenzel, G. H. Tolerances, covering systems, and the axiom of choice. Archivum mathematicum, Tome 25 (1989) no. 1-2, pp. 27-34. http://geodesic.mathdoc.fr/item/ARM_1989__25_1-2_a4/