Homotopy extension property

Homotopy extension property

In mathematics, in the area of algebraic topology, the homotopy extension property indicates when a homotopy can be extended to another one, so that the original homotopy is simply the restriction of the extended homotopy.

Definition

Given A subset X , we say that the pair mathbf{mathit{(A,X) has the homotopy extension property with respect to mathbf{mathit{Y if the following holds:

Given any continuous f: X o Y, g: A o Y for which there is a homotopy G: A imes I o Y of mathbf{mathit{f and mathbf{mathit{g, we can extend this to a homotopy F: X imes I o Y of mathbf{mathit{f and some mathbf{mathit{g', where g' : X o Y and g'mid A = g.

Other

If mathbf{mathit{(A,X) has the homotopy extension property independent of mathbf{mathit{Y, then the simple inclusion map i: A o X is a cofibration.

In fact, if you consider any cofibration i: Y o Z, then we have that mathbf{mathit{Y is homeomorphic to its image under mathbf{mathit{i. This implies that any cofibration can be treated as an inclusion map, and therefore it can be treated as having the homotopy extension property.

ee also

* Homotopy lifting property

References

*


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