Example 10.28.7. Let $A$ be a ring, $I \subset A$ an ideal, and $a \in A$ an element. There is a short exact sequence $0 \to A/(I : a) \to A/I \to A/(I, a) \to 0$ where the first arrow is given by multiplication by $a$. Thus if $P$ is a property of $A$-modules that is stable under extensions and holds for $0$, then the family of ideals $I$ such that $A/I$ has $P$ is an Oka family.
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