@article{MS2_1956__4_165625,
     author = {BJABNI J\'ONSSON},
     title = {Universal relational systems},
     journal = {Mathematica Scandinavica},
     pages = {193--208},
     publisher = {mathdoc},
     volume = {4},
     year = {1956},
     zbl = {0077.25302},
     url = {http://geodesic.mathdoc.fr/item/MS2_1956__4_165625/}
}