13A15 05C25 4 13A18 4 13B02 4 ring extension 4 05C99 3 zero-divisor graph 3 13C05 2 13C13 2 13H15 2 16D60 2 \(S\)-cotorsion-free module 2 \(S\)-second submodule 2 cancellation ideal 2 essential graph 2 pullback diagram 2 quasilocal ring 2 reduced ring 2 saturation 2 second submodule 2 simple module 2 special principal ideal ring 2 star operation 2 13F10 1 28A12 1 Clique number of a graph 1 Quasilocal ring 1 Special principal ideal ring 1 chromatic number 1 clique number of a graph 1