@article{CMUC_1971__12_3_a8,
     author = {Je\v{z}ek, Jaroslav},
     title = {Upper semicomplements and a definable element in the lattice of groupoid varieties},
     journal = {Commentationes Mathematicae Universitatis Carolinae},
     pages = {565--586},
     publisher = {mathdoc},
     volume = {12},
     number = {3},
     year = {1971},
     mrnumber = {0289398},
     zbl = {0225.08007},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/CMUC_1971__12_3_a8/}
}