This package for &GAP; 4 (at least version 4.4) implements set-theoretic unions of residue classes of the ring \mathbb{Z} of the integers, of its semilocalisations \Z_{(\pi)} at some finite set of primes \pi and of the polynomial rings GF(q)[x] for some prime power q as &GAP; domains and provides basic functionality for computing with these sets (intersection, union, difference etc., any of these also when one of the operands is a finite set of elements). It also implements the above-mentioned rings \Z_{(\pi)} as &GAP; domains.