Discussiones Mathematicae - General Algebra and Applications
Discussiones Mathematicae - General Algebra and Applications > 2000 > 20 > 1 > 87-95
Discussiones Mathematicae - General Algebra and Applications > 2000 > 20 > 2 > 219-231
Discussiones Mathematicae - General Algebra and Applications > 2002 > 22 > 2 > 183-198