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Notation:

We say two $C^1$ manifolds are $C^1$-homeomorphic if they are homeomorphic via a $C^1$ homeomorphism with $C^1$ inverse.

Question:

Let $n \geq 2$. Given a countable dense set of points $P \subset \mathbb R^n$, does there exist a $C^1$ foliation $M_{\alpha}$ of $\mathbb R^n$ by $C^1$ manifolds that are $C^1$-homeomorphic to $\mathbb R^{n-1}$ with the following property?

Suppose the foliation $M_{\alpha}$ is parametrised by $\alpha \in (0, 1)$. Then the set of all $\alpha$ such that $M_{\alpha} \cap P$ is dense in $M_{\alpha}$ is dense in $(0, 1)$.

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  • $\begingroup$ Do you happen to know the answer to a related simpler question: Given countable dense $P\subset\mathbb R^n$, there is at least one $C^1$-submanifold of $\mathbb R^n$ whose intersection with $P$ is dense? $\endgroup$
    – Wojowu
    Commented Apr 10, 2021 at 11:22
  • $\begingroup$ So, I think I can get at least a “$C^0$ + Lipschitz” manifold, but I have yet to even convince myself that even in the case of $\mathbb R^2$ that a $C^1$ manifold is possible. $\endgroup$
    – Nate River
    Commented Apr 10, 2021 at 13:33

1 Answer 1

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EDIT: Originally I could prove that there is such a foliation by topological manifolds:

Clearly, if $\mathbb{Q}^n$ is the set if points with all rational coordinates, you can have a foliation by parallel hyperplanes $H_\alpha$. Now, for any set $P$ there that is countable and dense there is homepmorphism $\Phi:\mathbb{R}^n\to\mathbb{R}^n$ such that $\Phi(\mathbb{Q}^n)=P$, see Claim A) on page 44 in [1]. Then $M_\alpha=\Phi(H_\alpha)$ is a foliation by topological manifolds.

However, as pointed out by Alessandro Codenotti in a comment below, Morayne proved in [2] that there is $\Phi$ with the properties listed above that is a volume preserving analytic diffeomorphism so in fact the foliation can be done by analytic manifolds.

[1] W. Hurewicz, H. Wallman, Dimension Theory. Princeton Mathematical Series, vol. 4. Princeton University Press, Princeton, N. J., 1941.

[2] M. Morayne, Measure preserving analytic diffeomorphisms of countable dense sets in $C^n$ and $R^n$. Colloq. Math. 52 (1987), 93–98.

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    $\begingroup$ For the $C^1$ case by a result of Morayne, see Measure preserving analytic diffeomorphisms of countable dense sets in Cn and Rn, Colloq. Math. 52 (1987), no. 1, 93–98. $\Phi$ can be chosen to be a diffeomorphism $\endgroup$ Commented Apr 10, 2021 at 17:31
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    $\begingroup$ @AlessandroCodenotti Wow!! That is a beautiful and a surprising result. $\endgroup$ Commented Apr 10, 2021 at 22:48

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