TY  - JOUR
AU  - Ježek, Jaroslav
TI  - Upper semicomplements and a definable element in the lattice of groupoid varieties
JO  - Commentationes Mathematicae Universitatis Carolinae
PY  - 1971
SP  - 565
EP  - 586
VL  - 12
IS  - 3
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/item/CMUC_1971__12_3_a8/
LA  - en
ID  - CMUC_1971__12_3_a8
ER  -