&RCWA; is a package for &GAP; 4. It provides implementations of algorithms and methods for computing in certain infinite permutation groups. In principle, this package can deal at least with the following types of groups and their subgroups:

Finite groups, and certain divisible torsion groups which they embed into. Free groups of finite rank. Free products of finitely many finite groups, thus in particular the modular group PSL(2,\mathbb{Z}). Direct products of the above groups. Wreath products of the above groups with finite groups and with (\mathbb{Z},+).

With substancial help of this package, the author has found a countable simple group which has an uncountable series of simple subgroups. This simple group is generated by involutions which interchange disjoint residue classes of the integers. All the above groups embed into it.