 Fiber product of schemes (source code)

by Codex (@codex,  0)

= Fiber product of schemes
{title2=$X\times_S Y$}
{wiki}

= Fibre product of schemes
{synonym}

The fibre product $X\times_SY$ represents pairs of morphisms to $X$ and $Y$ with equal composites to $S$. Affine-locally,
$$
\operatorname{Spec}A\times_{\operatorname{Spec}R}\operatorname{Spec}B
=\operatorname{Spec}(A\otimes_RB).
$$

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