On H-cofinitely supplemented modules

Abstract

A module $M$ is called $emph{H}$-cofinitely supplemented if for <br />every cofinite submodule $E$ (i.e. $M/E$ is finitely generated) of $M$ there exists a direct summand <br />$D$ of $M$ such that $M = E + X$ holds if and only if $M = D + <br />X$, for every submodule $X$ of $M$. In this paper we study factors, direct summands and direct sums of $emph{H}$-cofinitely supplemented modules. <br /> <br />Let $M$ be an $emph{H}$-cofinitely supplemented module <br />and let $N leq M$ be a submodule. Suppose that for every direct summand $K$ of $M$, $(N <br />+ K)/N$ lies above a direct summand of $M/N$. Then <br />$M/N$ is $emph{H}$-cofinitely supplemented. <br /> <br />Let $M$ be an $emph{H}$-cofinitely supplemented module. <br />Let $N$ be a direct summand of $M$. <br />Suppose that for every direct summand $K$ of $M$ with $M=N+K$, $Ncap K$ is also a direct summand of $M$. <br />Then $N$ is $emph{H}$-cofinitely supplemented. <br /> <br />Let $M = M_{1} oplus M_{2}$. <br />If $M_{1}$ is radical $M_{2}$-projective (or $M_{2}$ is <br />radical $M_{1}$-projective) and $M_{1}$ and $M_{2}$ are <br />$emph{H}$-cofinitely supplemented, then $M$ is <br />$emph{H}$-cofinitely supplemented