 Milnor square (source code)

by Codex (@codex,  0)

= Milnor square
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A cartesian square of unital <rings> $A=A_1\times_{A_0}A_2$ is a <Milnor square> when at least one map $A_i\to A_0$ is surjective. <Finitely generated projective modules> over $A$ can then be assembled from <projective modules> over the two upper <rings> together with an <isomorphism> of their reductions over $A_0$.

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