Daniele Micciancio Almost Perfect Lattices, the Covering Radius Problem, and Applications to Ajtai's Connection Factor. 118-169 2004 34 SIAM J. Comput. 1 http://epubs.siam.org/sam-bin/dbq/article/43351 db/journals/siamcomp/siamcomp34.html#Micciancio04