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Let there be a commutative diagram of abelian groups as below. If the two rows are exact and $\alpha$, $\beta$, $\delta$ and $\varepsilon$ are isomorphisms, then $\gamma$ is an isomorphism also

$$ \require{AMScd} \begin{CD} A @>{i }>> B @>{j }>> C @>{k }>> D @>{l }>> E \\ @V{\alpha}VV @V{\beta}VV @V{\gamma}VV @V{\delta}VV @V{\varepsilon}VV \\ A' @>{i'}>> B' @>{j'}>> C' @>{k'}>> D' @>{l }>> E' \\ \end{CD} $$

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