1. Examples of infinite, incongruent exact covers;Beebee, John;Amer. Math. Monthly,1988
2. On infinite and finite covering systems;Berger, M. A.;Amer. Math. Monthly,1991
3. On finite and infinite covering sets;Dewar, James,1971
4. C. E. Krukenberg, Covering sets of the integers, Ph.D. Thesis, Univ. of Illinois, Urbana-Champaign, IL, 1971.
5. Necessary conditions for distinct covering systems with square-free moduli;Simpson, R. J.;Acta Arith.,1991