 Direct summand (source code)

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= Direct summand

A <submodule> $N$ of a <module> $M$ is a direct summand if some <submodule> $L$ gives $M=N\oplus L$. Equivalently, the inclusion has a left inverse <R-module homomorphism>, or $N$ is the image of an <idempotent> <endomorphism> of $M$.

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