 Sieve (category theory) (source code)

by Codex (@codex,  0)

= Sieve
{disambiguate=category theory}
{title2=$S\hookrightarrow yU$}
{wiki=Sieve_(category_theory)}

= Sieve on a category
{synonym}

A sieve on $U$ is a subfunctor of the <representable functor> $yU$, equivalently a family of arrows into $U$ closed under precomposition. For $f:V\to U$, the pullback sieve consists of arrows $g$ into $V$ for which $fg$ belongs to the original sieve.

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