1. Perfect systems of difference sets - a survey;Abrham;Ars Combin.,1984
2. Symmetric bases of additive permutations;Abrham;Ars Combin.,1984
3. Additive permutations of an integer interval: symmetry and an estimate of their number;Abrham;Ars Combin.,1984
4. Remarks on the minimum number of components in perfect systems of difference sets;Abrham;Congress. Numer.,1986
5. Systèmes de triplets et différences associées;Bermond,1978