The Stacks project

Lemma 17.3.4. Let $j : U \to X$ be an open immersion of topological spaces. The functor $j_! : \textit{Ab}(U) \to \textit{Ab}(X)$ is exact.

Proof. Follows from the description of stalks given in Sheaves, Lemma 6.31.6. $\square$

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