1. Perfect systems of difference sets—a survey;Abrham;Ars Combinatoria,1984
2. Symmetric bases of additive permutations;Abrham;Ars Combinatoria,1984
3. Additive permutations of an integer interval: symmetry and an estimate of their number;Abrham;Ars Combinatoria,1984
4. Remarks on the minimum number of components in perfect systems of difference sets;Abrham;Congressus Numerantiuum,1986
5. On a conjecture of Paul Erdös for perfect systems of difference sets;Laufer;Discrete Math.,1983