@article{BAG_1991__31_138482,
     author = {H.-J. Vogel},
     title = {On clones of relations},
     journal = {Beitr\"age zur Algebra und Geometrie},
     pages = {179--192},
     publisher = {mathdoc},
     volume = {31},
     year = {1991},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/BAG_1991__31_138482/}
}