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12 votes
2 answers
685 views

Is the square root of a monotonic function whose all derivatives vanish smooth?

I think that there is a chance for smoothness under the additional assumption that $g^{(k)}>0$ in a neighbourhood of zero for every $k$, but I am not sure. …
20 votes
5 answers
2k views

Smoothness of the closest point on a submanifold

Let $(M,g)$ be a smooth Riemannian manifold, and let $S \subseteq M$ be a compact submanifold. Assume that for each $p \in M$, there exist a unique closest point on $S$, i.e a unique point $\tilde s …
21 votes
1 answer
1k views

A differentiable isometry is smooth?

I posted this question in MSE but got no response (even after giving a bounty), so I am trying here. Let $M,N$ be smooth $d$-dimensional Riemannian manifolds. Suppose $f:M \to N$ is a differentiable …
7 votes
1 answer
373 views

Are metric isometries smooth at the boundary?

Let $M,N$ be smooth Riemannian manifolds with boundary (In particular, we assume the boundaries are smooth). Suppose we have a map $\phi:M \to N$ which satisfies the following properties: $$(1) \, \ …
0 votes

Smoothness of the closest point on a submanifold

$\newcommand{\til}{\tilde}$ This is an attempt to prove rigorously that there exists an open subset $\Omega$ of the normal bundle to $S$, such that $exp:\Omega \to M$ is a bijection. This proof seems …
Asaf Shachar's user avatar
  • 6,741
0 votes
0 answers
320 views

Unit sphere of a norm is a submanifold implies the norm is smooth?

Let us call a norm on $\mathbb{R}^n$ smooth if its restriction $\| \cdot \|:\mathbb{R}^n\setminus \{ 0 \} \to \mathbb{R}$ is a smooth map. Suppose the unit sphere of a norm $\| \cdot \|$ is an embedd …