@article{10_21136_CMJ_1992_128368,
     author = {Raftery, J. G. and Sturm, T.},
     title = {Tolerance numbers, congruence $n$-permutability and {BCK-algebras}},
     journal = {Czechoslovak Mathematical Journal},
     pages = {727--740},
     publisher = {mathdoc},
     volume = {42},
     number = {4},
     year = {1992},
     doi = {10.21136/CMJ.1992.128368},
     mrnumber = {1182203},
     zbl = {0784.08002},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.21136/CMJ.1992.128368/}
}