join
Given two topological spaces X and Y, their join, denoted by X⋆Y, is defined to be the quotient space
X⋆Y:=X×[0,1]×Y/∼, |
where the equivalence relation ∼ is generated by
(x,0,y1) | ∼(x,0,y2) | for anyx∈X,y1,y2∈Y,and | ||
(x1,1,y) | ∼(x2,1,y) | for anyy∈Y,x1,x2∈X. |
Intuitively, X⋆Y is formed by taking the disjoint union of the two spaces and attaching a line segment joining every point in X to every point in Y.
Some examples:
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The join of a space X with a one-point space is called the cone of X.
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The join of the spheres Sn and Sm is the sphere Sn+m+1.
Title | join |
---|---|
Canonical name | Join1 |
Date of creation | 2013-03-22 13:25:40 |
Last modified on | 2013-03-22 13:25:40 |
Owner | mathcam (2727) |
Last modified by | mathcam (2727) |
Numerical id | 7 |
Author | mathcam (2727) |
Entry type | Definition |
Classification | msc 54B99 |
Related topic | Cone |
Related topic | Suspension![]() |
Defines | join |