 Solution (source code)

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= Solution

A <morphism of schemes> $f:X\to Y$ is a <separated morphism> if its <diagonal morphism>
$$
\boxed{\Delta_f:X\longrightarrow X\times_YX}
$$
is a <closed immersion>. The <diagonal morphism> is induced by the pair of identity maps on $X$. Thus separatedness is a condition relative to the given target $Y$, not a requirement that $X$ be absolutely separated.

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