$\def\cube{\mathbf Q}$Let $\cube$ be the Hilbert cube. Give an example of a closed subset $B$ of $\cube$ such that $\operatorname{Int}(B) = \emptyset$ and $B$ is not a z-set.


If anyone has any idea to solve this problem, it would help me a lot. I write down some information:


**Definition**. Let $\cube= \prod\_{n=1}^{\infty} [0,1]$ with product topology), with metric $d$ such that if $(x\_n)\_n, (y\_n)\_n \in \cube$, $d((x\_n)\_n,(y\_n)\_n) = \sum\_{n=1}^{\infty} \frac{\lvert x\_n - y\_n\rvert}{2^n}$. Then $B \subseteq \cube$ is a z-set if, for each $\epsilon > 0$, there is a continuous function $f\_\epsilon$ from $\cube$ to $\cube \setminus B$ such that $d(f\_\epsilon(x),x) < \epsilon$ for all $x \in X$.


I have tried the following, where a $\sigma$z-set is a countable union of z-sets. (In $\cube$, I think that all $\sigma$z-sets are z-sets.)


**Lemma**. If $B \subseteq \cube$ is a $\sigma$z-set, then $\cube \setminus B$ is a topologically complete, separable metric AR (Absolute Retract).


**Note**. In $\cube$, $B'$ being a retract is equivalent to $B'$ being AR.


Then, I have tried to find an example of a $B \subseteq \cube$ such that $\cube \setminus B$ is not a retract. By the lemma, this $B$ would not be a $\sigma$z-set. Then check if this set $B$ has empty interior in $\cube$ and is closed. I could not find such a $B$.


References.


[1] Alejandro Wanes, Sam Nadler Jr. HYPERSPACES: Fundamental and Recent Advances.


[2] [Macías - Una introducción a los retractos absolutos y a los retractos de vecindad absolutos](http://www.scielo.org.co/pdf/rein/v31n2/v31n2a05.pdf).



A closed subset $B$ of the Hilbert cube such that $\operatorname{Int}(B) = \emptyset$ and $B$ is not a z-set
$A=\{0\} \times [-1,1]^{\Bbb N}$ works as an example, e.g.


For more info on $Z$-sets in $Q$, see *Infinite-dimensional Topology* by Jan van Mill.


