@article{SF_1989__38_2_134967,
     author = {K.H. Hofmann and W.A.F. Ruppert},
     title = {Foliations induced by congruences.},
     journal = {Semigroup forum},
     pages = {365--370},
     publisher = {mathdoc},
     volume = {38},
     number = {2},
     year = {1989},
     zbl = {0663.22001},
     url = {http://geodesic.mathdoc.fr/item/SF_1989__38_2_134967/}
}