Corollary 1

Tag 0DZP, permanent. Cite it as [Bourbaki, Tag 0DZP].

Consider a commutative diagram with exact rows

\begin{array}{cccccccccccc} 0 & \rightarrow & N & \rightarrow & R_n & \rightarrow & \cdots \rightarrow & R_1 & \rightarrow & M & \rightarrow & 0 \\ \downarrow & & \downarrow & & \downarrow & & & \downarrow & & \downarrow & & \downarrow \\ 0 & \rightarrow & N & \rightarrow & R'_n & \rightarrow & \cdots \rightarrow & R'_1 & \rightarrow & M & \rightarrow & 0 ; \end{array}

the two rows of the diagram have the same associated class in $\mathrm{Ext}_A^n(M, N)$ .

Bourbaki puts the proof directly after the statement, so what is above is the statement and its proof together.

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