@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/}
}