
Lemma 10.88.6. Let $M$ be a flat Mittag-Leffler module over $R$. Let $F$ be an $R$-module and let $x \in F \otimes _ R M$. Then there exists a smallest submodule $F' \subset F$ such that $x \in F' \otimes _ R M$.

Proof. Since $M$ is flat we have $F' \otimes _ R M \subset F \otimes _ R M$ if $F' \subset F$ is a submodule, hence the statement makes sense. Let $I = \{ F' \subset F \mid x \in F' \otimes _ R M\}$ and for $i \in I$ denote $F_ i \subset F$ the corresponding submodule. Then $x$ maps to zero under the map

$F \otimes _ R M \longrightarrow \prod (F/F_ i \otimes _ R M)$

whence by Proposition 10.88.5 $x$ maps to zero under the map

$F \otimes _ R M \longrightarrow \left(\prod F/F_ i\right) \otimes _ R M$

Since $M$ is flat the kernel of this arrow is $(\bigcap F_ i) \otimes _ R M$ which proves the lemma. $\square$

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