&ResClasses; is a package for &GAP; 4, which provides a fully-featured and easy-to-use implementation of set-theoretic unions of residue classes of the integers and of a few other rings.

The class of sets which &ResClasses; can deal with includes the open and the closed sets in the topology on the respective ring which is induced by taking the set of all residue classes as a basis, as far as the usual restrictions imposed by the finiteness of computing resources permit this.

The package further provides slightly more specialized functionality for unions of residue classes with distinguished representatives and signed moduli.

The &ResClasses; package is used in a group theoretical context by the &RCWA; package .