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I am reading J A Beachy's Book, Introductory Lectures on Rings and Modules"... ...
I am currently focused on Chapter 2: Modules ... and in particular Section 2.4: Chain Conditions ...
I need help with the proof of Proposition 2.4.5 ...Proposition 2.4.5 reads as follows:
View attachment 6041
https://www.physicsforums.com/attachments/6042
In the above text by Beachy ... in the proof of part (a) ... we read the following:"... ... ... Conversely, assume that $$N$$ and $$M/N$$ are Noetherian, and let $$M_0$$ be a submodule of $$M$$. Then $$M_0 \cap N$$ and $$M_0 / ( M_0 \cap N ) \cong (M_0 + N) / N$$ are both finitely generated, so $$M_0$$ is finitely generated ... ... ... "
I am very unsure of this part of the proof ... but overall Beachy seems to be trying to prove that an arbitrary submodule of $$M$$, namely $$M_0$$, is finitely generated ... ... and this means that M is Noetherian ... (Beachy, in his Proposition 2.4.3 has shown that every submodule of $$M$$ being finitely generated is equivalent to M being Noetherian ... ... )BUT ... I do not see how it follows in the above that ... ... $$M_0 \cap N$$ and $$M_0 / ( M_0 \cap N ) \cong (M_0 + N) / N$$ are both finitely generated ... ... AND ... exactly why it then follows that $$M_0$$ is finitely generated ... ...
Hope someone can help ...
Peter
I am currently focused on Chapter 2: Modules ... and in particular Section 2.4: Chain Conditions ...
I need help with the proof of Proposition 2.4.5 ...Proposition 2.4.5 reads as follows:
View attachment 6041
https://www.physicsforums.com/attachments/6042
In the above text by Beachy ... in the proof of part (a) ... we read the following:"... ... ... Conversely, assume that $$N$$ and $$M/N$$ are Noetherian, and let $$M_0$$ be a submodule of $$M$$. Then $$M_0 \cap N$$ and $$M_0 / ( M_0 \cap N ) \cong (M_0 + N) / N$$ are both finitely generated, so $$M_0$$ is finitely generated ... ... ... "
I am very unsure of this part of the proof ... but overall Beachy seems to be trying to prove that an arbitrary submodule of $$M$$, namely $$M_0$$, is finitely generated ... ... and this means that M is Noetherian ... (Beachy, in his Proposition 2.4.3 has shown that every submodule of $$M$$ being finitely generated is equivalent to M being Noetherian ... ... )BUT ... I do not see how it follows in the above that ... ... $$M_0 \cap N$$ and $$M_0 / ( M_0 \cap N ) \cong (M_0 + N) / N$$ are both finitely generated ... ... AND ... exactly why it then follows that $$M_0$$ is finitely generated ... ...
Hope someone can help ...
Peter