Gift Wrap Theorem
No subspace of R^n can be homeomorphic to S^n.
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References
Dodson, C. T. J. and Parker, P. E. A User's Guide to Algebraic Topology. Dordrecht, Netherlands: Kluwer, p. 121, 1997.Referenced on Wolfram|Alpha
Gift Wrap TheoremCite this as:
Weisstein, Eric W. "Gift Wrap Theorem." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/GiftWrapTheorem.html