@misc{AMUC_1990__56-57_186064,
     title = {[unknown]},
     journal = {Acta mathematica Universitatis Comenianae},
     pages = {249--259},
     year = {1990},
     volume = {56-57},
     url = {http://geodesic.mathdoc.fr/item/AMUC_1990__56-57_186064/}
}