1. Disjoint covering systems with precisely one multiple modulus;Berger;Acta. Arith.,1988
2. New results for covering systems of residue sets;Berger;Bull. Amer. Math. Soc. (N.S.),1986
3. Roots of unity and covering sets;Newman;Math. Ann.,1971
4. Generalizations of some results for exactly covering systems;Porubský;Mat. Casopis Sloven. Akad.,1972
5. Results and problems on covering systems of residue classes;Porubský;Mitt. Math. Sem. Giessen,1981