We study the lattice L(RSn) of subvarieties of the variety of semigroups generated by completely 0-simple semigroups over groups with exponent dividing n, with a particular focus on the lattice LE(RSn) consisting of those varieties that are generated by completely 0-simple semigroups. The sublattice of LE(RSn) consisting of the aperiodic varieties is described and several endomorphisms of L(RSn) considered. The complete congruence on LE(RSn) that relates varieties containing the same aperiodic completely 0-simple semigroups is considered in some detail.
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