Discussiones Mathematicae - General Algebra and Applications
Discussiones Mathematicae - General Algebra and Applications > 2001 > 21 > 2 > 201-205
Discussiones Mathematicae - General Algebra and Applications > 2014 > 34 > 2 > 213-219
Discussiones Mathematicae - General Algebra and Applications > 2015 > 35 > 2 > 119-128