nLab homotopy product



Homotopy theory

homotopy theory, (∞,1)-category theory, homotopy type theory

flavors: stable, equivariant, rational, p-adic, proper, geometric, cohesive, directed

models: topological, simplicial, localic, …

see also algebraic topology



Paths and cylinders

Homotopy groups

Basic facts


Limits and colimits



Homotopy products are Cartesian products in homotopy theory, hence are a special case of homotopy limits for the case that the the indexing diagram is a discrete category.


In any model category, the homotopy product of a family of objects {A i} iI\{A_i\}_{i\in I} can be computed by fibrantly replacing each A iA_i and computing the (ordinary) Cartesian product of the resulting family {RA i} iI\{\mathrm{R}A_i\}_{i\in I} of fibrant objects.



(homotopy products of simplicial sets)
In simplicial sets with simplicial weak equivalences (as in the classical model structure on simplicial sets), finite homotopy products can be computed by taking their (ordinary) Cartesian product, because finite products preserve simplicial weak equivalences. More generally, homotopy products can be computed by applying Kan’s Ex^∞ functor to each simplicial set and taking their (ordinary) Cartesian product.


(homotopy products of topological space)
In topological spaces with weak homotopy equivalences, as in the classical model structure on topological spaces, every object is fibant, so that homotopy products can be computed as ordinary Cartesian products, which here means product spaces.


The same applies to the relative category of chain complexes of abelian groups and quasi-isomorphisms (Grothendieck 1957, section 1.5),

One way to see this is that in the projective model structure on chain complexes (when it exists) again every object is a fibrant object.


Last revised on July 9, 2021 at 12:19:24. See the history of this page for a list of all contributions to it.