Discussiones Mathematicae - General Algebra and Applications
Discussiones Mathematicae - General Algebra and Applications > 2001 > 21 > 2 > 239-253
Discussiones Mathematicae - General Algebra and Applications > 2003 > 23 > 1 > 63-79
Discussiones Mathematicae - General Algebra and Applications > 2004 > 24 > 1 > 115-124