TY - JOUR AU - Pondělíček, Bedřich TI - A Relation for Closure Operations on a Semigroup JO - Mathematica slovaca PY - 1973 SP - 249 EP - 256 VL - 23 IS - 3 UR - http://geodesic.mathdoc.fr/item/MASLO_1973_23_3_a7/ LA - en ID - MASLO_1973_23_3_a7 ER -