# Contents

## Idea

The “classical homotopy category” $Ho(Top)$ typically refers to the category of topological spaces with morphisms between them the homotopy classes of continuous functions, or (slightly less classically but more commonly these days) to its full subcategory on those topological spaces homeomorphic to a CW-complex. The latter is technically the homotopy category obtained by localizing the category of topological spaces at those continuous functions that are weak homotopy equivalences, hence it is also the homotopy category of a model category of the classical model structure on topological spaces.

## Definition

By $Ho(Top)$ one denotes the category which is the homotopy category of Top with respect to weak equivalences given

Depending on context here Top contains all topological spaces or is some subcategory of nice topological spaces.

The study of $Ho(Top)$ was the motivating example of homotopy theory. Often $Ho(Top)$ is called the homotopy category.

The simplicial localization of Top at the weak homotopy equivalences yields the (∞,1)-category of ∞-groupoids/homotopy types.

## Compactly generated spaces

Let now $Top$ denote concretely the category of compactly generated weakly Hausdorff spaces. And Let $CW$ be the subcategory on CW-complexes. We have $Ho(CW)_{whe} = Ho(CW)_{he} = Ho(CW)$.

There is a functor

$Top \to Ho(CW)$

that sends each topological space to a weakly homotopy equivalent CW-complex.

By the homotopy hypothesis-theorem $Ho(CW)$ is equivalent for instance to the homotopy category of a model category $Ho(sSet_{Quillen})$ of the classical model structure on simplicial sets as well as $Ho(Top_{Quillen})$of the classical model structure on topological spaces.

## Shape theory

The category $Ho(Top)_{he}$ can be studied by testing its objects with objects from $Ho(CW)$. This is the topic of shape theory.

## Related concepts

category: category

Last revised on April 26, 2018 at 01:57:45. See the history of this page for a list of all contributions to it.