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I am reading Paul E. Bland's book, "Rings and Their Modules".
I am trying to understand Chapter 4, Section 4.2 on Noetherian and Artinian modules and need help with the proof of $$ (2) \Longrightarrow (3) $$ in Proposition 4.2.3.
Proposition 4.2.3 and its proof read as follows:
View attachment 3658
View attachment 3659
In the proof of $$ (2) \Longrightarrow (3) $$ we read:
" ... ... If $$N^* \ne N$$, let $$x \in N - N^*$$.
Then $$N^* + xR$$ is a finitely generated submodule of N that properly contains $$N^*$$ ... ..."
My question is as follows
ow does it follow from $$N^* \ne N$$ and $$x \in N - N^*$$ ... ...
... that ...
... ... $$N^* + xR$$ is a finitely generated submodule of N that properly contains $$N^*$$?
Hope someone can help ... ...
Peter***EDIT***
It is certainly the case that $$N^*$$ is finitely generated since it belongs to $$\mathscr{S}$$ and so it seems obvious that $$N^* + xR$$ is finitely generated ... but is it a submodule? Presumably it is a module because $$N^*$$ and $$xR$$ are modules and the sum of two modules is a module ... but how are we sure that it is a submodule of $$N$$ ...
It certainly also seems that $$N^* + xR$$ properly contains $$N^*$$ ...
... so I am really close to feeling I understand the answer to my question ...
Can someone please critique my thinking?
I am trying to understand Chapter 4, Section 4.2 on Noetherian and Artinian modules and need help with the proof of $$ (2) \Longrightarrow (3) $$ in Proposition 4.2.3.
Proposition 4.2.3 and its proof read as follows:
View attachment 3658
View attachment 3659
In the proof of $$ (2) \Longrightarrow (3) $$ we read:
" ... ... If $$N^* \ne N$$, let $$x \in N - N^*$$.
Then $$N^* + xR$$ is a finitely generated submodule of N that properly contains $$N^*$$ ... ..."
My question is as follows

... that ...
... ... $$N^* + xR$$ is a finitely generated submodule of N that properly contains $$N^*$$?
Hope someone can help ... ...
Peter***EDIT***
It is certainly the case that $$N^*$$ is finitely generated since it belongs to $$\mathscr{S}$$ and so it seems obvious that $$N^* + xR$$ is finitely generated ... but is it a submodule? Presumably it is a module because $$N^*$$ and $$xR$$ are modules and the sum of two modules is a module ... but how are we sure that it is a submodule of $$N$$ ...
It certainly also seems that $$N^* + xR$$ properly contains $$N^*$$ ...
... so I am really close to feeling I understand the answer to my question ...
Can someone please critique my thinking?
Last edited: