nLab
sifted (infinity,1)-category

Contents

Definition

Definition

An (∞,1)-category is sifted if a quasi-category KsSetK \in sSet modelling it has the property that

  1. it is not empty, KK \neq \emptyset

  2. The diagonal KK×KK \to K \times K (in sSet) models a cofinal (∞,1)-functor.

Properties

Proposition

Let CC be an (∞,1)-category such that products preserve sifted (∞,1)-colimits (for instance an (∞,1)-topos, see universal colimits).

Then sifted (∞,1)-colimits preserve finite products.

This is (Lurie, lemma 5.5.8.11).

Examples

General

Proposition

The opposite category Δ op\Delta^{op} of the simplex category is a sifted (,1)(\infty,1)-category.

Proposition

Every filtered (∞,1)-category is sifted.

This appears as (Lurie, prop. 5.3.1.20).

In categories of commutative monoids

Proposition

In a category of commutative monoids in a symmetric monoidal (,1)(\infty,1)-category, sifted colimits are computed as sifted colimits in the underlying (,1)(\infty,1)-category.

See commutative monoid in a symmetric monoidal (∞,1)-category for details.

References

Section 5.5.8 of

Revised on May 4, 2012 00:25:53 by Urs Schreiber (89.204.137.201)