C^infty on U: Question & Counter Example

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SUMMARY

The discussion centers on the differentiability of functions, specifically whether a function f is C^infty on an open set U given that both h and h o f are C^infty on f(U) and U, respectively. A user acknowledges a misunderstanding, stating that the assumption is trivially false by providing a counterexample where h is a constant function. The conclusion emphasizes that the initial assumption does not hold under the given conditions.

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Palindrom
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Suppose h and h o f are both C^infty on f(U) and U correspondingly, with U an open set. Assume now that f(U) is open. Is f C^infty on U? Does anyone have a counter example?

I've edited the question so that it would actually make sense.
 
Last edited:
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trivially false. take h constant.
 
How very stupid of me. Thank you.
 

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