@article{01990002,
title = {Composite covering systems of minimum cardinality.},
journal = {Integers},
volume = {3},
year = {2003},
zbl = {1028.11006},
language = {en},
url = {http://dml.mathdoc.fr/item/01990002}
}
Jenkin, Scott; Simpson, Jamie. Composite covering systems of minimum cardinality.. Integers, Tome 3 (2003) . http://gdmltest.u-ga.fr/item/01990002/