Discussiones Mathematicae - General Algebra and Applications
Discussiones Mathematicae - General Algebra and Applications > 2005 > 25 > 1 > 23-37
Discussiones Mathematicae - General Algebra and Applications > 2006 > 26 > 1 > 85-109
Discussiones Mathematicae - General Algebra and Applications > 2009 > 29 > 2 > 81-107