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This is a weak version of this problem, written down in Lviv Scottish Book.

I start with necessary definitions.

Let $K=-K$ be a centrally symmetric compact convex body in the Euclidean space $\mathbb R^n$, and $\partial K$ be the boundary of $K$ in $\mathbb R^n$.

Definition. A 1-dimensional linear subspace $L\subset \mathbb R^n$ is called an $K$-admissible direction if for every $x\in\partial K$ the intersection $\partial K\cap(x+L)$ contains at most two points. It this case we can define the map $\theta_L:\partial K\to\partial K$ assigning to every point $x\in\partial L$ the unique point $\theta_L(x)$ such that $\partial K\cap(x+L)=\{x,\theta_L(x)\}$.

Remark 1. By the answer to this MO-question, the set of $K$-admissible directions is dense in the space $Gr(1,\mathbb R^n)$ of all 1-dimensional linear subspaces of $\mathbb R^n$.

Problem. Are there $K$-admissible directions $L_1,\dots,L_m$ such that the map $$\theta_{L_m}\circ \dots\circ \theta_{L_1}:\partial K\to\partial K$$ has no fixed points?

Remark 2. For $n=2$ the answer to this problem is affirmative with $m=n=2$.

Example. For the convex body $K=[-1,1]^2$ in $\mathbb R^2$ and the special directions $L_1=\{(x,y)\in\mathbb R^2:x-y=0\}$ and $L_2=\{(x,y)\in\mathbb R^2:x+y=0\}$, the map $\theta_{L_2}\circ\theta_{L_1}:\partial K\to\partial K$ has no fixed points.

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  • $\begingroup$ Any comments on my question mathoverflow.net/q/391839/121665? $\endgroup$ Commented May 4, 2021 at 12:53
  • $\begingroup$ @PiotrHajlasz I made a comment, but not very valuable (probably it should be deleted). Concerning you question, I have never seen such result and it is not obvious (for $n>1$). $\endgroup$ Commented May 5, 2021 at 5:10

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