nLab
finite (infinity,1)-limit

Context

(,1)(\infty,1)-Category theory

Limits and colimits

Finite (,1)(\infty,1)-limits

Definition

A finite (,1)(\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 (,1)(\infty,1)-limits

Proposition

An (∞,1)-functor F:CDF : C \to D out of an (∞,1)-category CC that has all finite (,1)(\infty,1)-limits preserves these finite (,1)(\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 CC be a small (∞,1)-category with finite (,1)(\infty,1)-limits, and H\mathbf{H} an (∞,1)-topos. Write PSh(C)PSh(C) for the (∞,1)-category of (∞,1)-presheaves on CC.

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

This appears as (Lurie, prop. 6.1.5.2).

Examples

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

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

References

Revised on June 19, 2013 12:25:41 by Urs Schreiber (82.169.65.155)