closure operator 16D90 5 16S90 5 preradical 4 06B23 3 module 3 ring 3 adjoint functors 2 category of modules 2 closed submodule 2 dense submodule 2 lattice 2 lattice of submodules 2 06A15 1 18A40 1 18E40 1 20F18,20F05,20F24,16D10 1 Property R 1 Property S 1 commensurable 1 hereditary ( cohereditary) closure operator 1 lattice operations 1 natural transformation 1 product ( coproduct) of closure operators 1 variety of groups 1