\begin{tikzcd}
	0 && {M \intersect N} && {M \oplus N} && {M+N} && 0
	\arrow[from=1-1, to=1-3]
	\arrow["{\iota_M \oplus \iota_N}", from=1-3, to=1-5]
	\arrow["{(m,n)\mapsto m-n}", from=1-5, to=1-7]
	\arrow[from=1-7, to=1-9]
\end{tikzcd}

> [Link to Diagram](https://q.uiver.app/?q=WzAsNSxbMCwwLCIwIl0sWzIsMCwiTSBcXGludGVyc2VjdCBOIl0sWzQsMCwiTSBcXG9wbHVzIE4iXSxbNiwwLCJNK04iXSxbOCwwLCIwIl0sWzAsMV0sWzEsMiwiXFxpb3RhX00gXFxvcGx1cyBcXGlvdGFfTiJdLFsyLDMsIihtLG4pXFxtYXBzdG8gbS1uIl0sWzMsNF1d)

![](attachments/Pasted%20image%2020220203132114.png)

$$
0 \rightarrow R /(I: a) \stackrel{a}{\rightarrow} R / I \rightarrow R /(I+(a)) \rightarrow 0
$$