%0 Journal Article %A Wilce, Alexander %T Perspectivity and congruence in partial abelian semigroups %J Mathematica slovaca %D 1998 %P 117-135 %V 48 %N 2 %I mathdoc %U http://geodesic.mathdoc.fr/item/MASLO_1998__48_2_a1/ %G en %F MASLO_1998__48_2_a1