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Definition: Let $M$ be an $R$-module. Then

  1. A submodule $N$ is called small (in $M$) if $N+K=M\implies K=M,\forall K\leq M$.
  2. A submodule $N$ is called a supplement of a submodule $K$ (in $M$) if $N$ is minimal with respect to the property $N+K=M$.
  3. A submodule $N$ is called a supplement submodule if it is a supplement of some submodule $K$.

My Question: Does every mon-small submodule contain a nonzero supplement submodule of the module.

1 Answers1

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False.

You can take example of $\mathbb{Z}$-module $\mathbb{Z}$. Its every nonzero submodule is nonsmall while it has no nonzero supplement submodule.

bipin
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