Discussiones Mathematicae - General Algebra and Applications
Discussiones Mathematicae - General Algebra and Applications > 2000 > 20 > 1 > 97-120
Discussiones Mathematicae - General Algebra and Applications > 2007 > 27 > 1 > 11-19
Discussiones Mathematicae - General Algebra and Applications > 2010 > 30 > 2 > 207-215