TY - JOUR AU - Wilce, Alexander TI - Perspectivity and congruence in partial abelian semigroups JO - Mathematica slovaca PY - 1998 SP - 117 EP - 135 VL - 48 IS - 2 UR - http://geodesic.mathdoc.fr/item/MASLO_1998_48_2_a1/ LA - en ID - MASLO_1998_48_2_a1 ER -