nLab finite (infinity,1)-limit

Finite -limits

Context

$(\infty,1)$-Category theory

(∞,1)-category theory

Models

Limits and colimits

limits and colimits

Finite $(\infty,1)$-limits

Definition

A finite $(\infty,1)$-limit is an (∞,1)-limit over a finitely presented (∞,1)-category – a finite (∞,1)-category.

If we model our (∞,1)-categories by quasicategories, then this can be made precise by saying it is a limit over some simplicial set with finitely many nondegenerate simplices. Note that such a simplicial set is rarely itself a quasicategory; we regard it instead as a finite presentation of a quasicategory.

Properties

Preservation of finite $(\infty,1)$-limits

Proposition

An (∞,1)-functor $F : C \to D$ out of an (∞,1)-category $C$ that has all finite $(\infty,1)$-limits preserves these finite $(\infty,1)$-limits as soon as it preserves (∞,1)-pullbacks and the terminal object.

This appears as (Lurie, cor. 4.4.2.5).

Proposition

Let $C$ be a small (∞,1)-category with finite $(\infty,1)$-limits, and $\mathbf{H}$ an (∞,1)-topos. Write $PSh(C)$ for the (∞,1)-category of (∞,1)-presheaves on $C$.

If a functor $F : PSh_\infty(C) \to \mathbf{H}$ preserves (∞,1)-colimits and finite $(\infty,1)$-limits of representables, then it preserves all finite $(\infty,1)$-limits.

This appears as (Lurie, prop. 6.1.5.2).

Examples

• Binary products, pullbacks, and terminal objects are all finite $(\infty,1)$-limits.

• Unlike the case in 1-category theory, the splitting of idempotents is not a finite $(\infty,1)$-limit.

References

Relation to homotopy type theory:

Last revised on September 28, 2017 at 12:30:29. See the history of this page for a list of all contributions to it.