When an $\mathcal{S}$-closed submodule is a direct summand

Abstract

It is well known that a direct sum of CLS-modules is not, in general, a CLS-module. It is proved that if $M=M_1\oplus M_2$, where $M_1$ and $M_2$ are CLS-modules such that $M_1$ and $M_2$ are relatively ojective (or $M_1$ is $M_2$-ejective), then $M$ is a CLS-module and some known results are generalized. Tercan [8] proved that if a module $M=M_1\oplus M_2$ where $M_1$ and $M_2$ are CS-modules such that $M_1$ is $M_2$-injective, then $M$ is a CS-module if and only if $Z_2(M)$ is a CS-module. Here we will show that Tercan's claim is not true.

arXiv comment8 pages