Is There a Smooth Map from S^n to the Equator E of S^n for n ≥ 2?

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The discussion addresses the existence of a smooth map f: S^n → E, where E is the equator of S^n, for n ≥ 2. It concludes that such a function cannot exist, as demonstrated through homology theory and the properties of diffeomorphisms. The argument hinges on the contradiction arising from the degree of the restriction of the map, leading to an absurdity in the homological diagram. This establishes that there is no retraction from the n-disk to its boundary in this context.

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For n\geq 2, is there a smooth map f: S^n\rightarrow E (E is the equator of S^n) which has the property that the restriction of f to E is a diffeomorphism from E to E?
 
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Do you know how to prove using homology theory that there is no retraction from the n-disk to its boundary? It is the same here:

Suppose such a function f exists. Call g the restriction of f to the northern hemisphere of S^n which we will regard as the n-disk D^n. Call h the restriction of g to E. By hypothese, h is a diffeo and so has degree ±1. The following diagram commute:

D^n<---E
|...|
|g...| h
|...|
E<-------|

that is, g o i = h where i is the inclusion of E in D^n. Passing to the realm of (n-1)-degree homology, the above diagram becomes the following comutative diagram

0<------Z
|...|
|...| ±1
|...|
Z<-------|

which is absurd.
 
Thanks a lot!
 

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