%0 Journal Article %A I. V. Protasov %T Points of joint continuity for theĀ semigroup of ultrafilters on anĀ Abelian group %J Sbornik. Mathematics %D 1996 %P 287-296 %V 187 %N 2 %U http://geodesic.mathdoc.fr/item/SM_1996_187_2_a6/ %G en %F SM_1996_187_2_a6