&ResClasses; is a package for &GAP; 4 which implements set-theoretic unions of residue classes of the ring of integers, of its semilocalisations and of univariate polynomial rings over finite fields as &GAP; domains.

It provides basic functionality for computing with these sets, like forming intersections, unions and differences. It supports these operations also in the case that one of the operands is a finite set of ring elements. The package further implements the mentioned semilocalisations \Z_{(\pi)} of \Z as &GAP; domains.