Schur rings over free Abelian group of rank two.

Schur rings are subrings of the group ring of the group G afforded by a partition of G into finite sets. In this paper, Schur rings over a free abelian group of rank two are classified under the assumption that one of the direct factors is a union of some basic sets. There are eight different types, and all but one type of which are traditional. [ABSTRACT FROM AUTHOR]