Let $D\subset \Bbb{R}$ be a dense set.
Question: Does $D$ intersect every closed uncountable sets?
The answer is negative. As the Cantor set $\mathcal{C}$ is n.w.dense , it's exterior $\Bbb{R}\setminus \overline{\mathcal{C}}=\Bbb{R}\setminus {\mathcal{C}}$ is dense in $\Bbb{R}$ but it doesn't intersect the closed uncountable set $\mathcal{C}$.
Here we want to focus on non measurable dense sets.
Under what assumption on the the dense set makes the desirable conclusion true?
$A\subset \Bbb{R}$ is called saturated non measurable set iff$$m_i(A) =0=m_i(A^c)$$
Where $m_i(A) $ is the inner measure of $A$ and $A^c=\Bbb{R}\setminus A$
For an example Bernstein set is a saturated non measurable set.
Claim: $A\subset \Bbb{R}$ be a saturated non measurable set then $A$ is dense.
Lemma: Let $A\subset \Bbb{R}$ be such that $m_i(A^c) =0$.Then $\forall E\in\mathcal{L}(\Bbb{R}) $ with $m(E) >0$ we have $A\cap E\neq \emptyset$
Proof (of the Lemma): Assume the contrary that is $A\cap E=\emptyset$.
Then $E\subset A^c$ implies $m_i(A^c)\ge m_i(E)=m(E) >0$.
This contradict our assumption that $m_i(A^c) =0$
Proof (of the claim) : Any non empty open interval $(a, b) $ is a measurable set with positive measure. Hence from the above Lemmma , it is clear that $A\cap (a, b) \neq \emptyset$.
Hence $A$ is dense in $\Bbb{R}$
Let $A\subset \Bbb{R}$ be a saturated non measurable set.
Question: Does $A$ intersect every closed uncountable sets?
Bernstein set is an example of a saturated non measurable set and Bernstein set intersect every closed uncountable sets.
Conjecture : A saturated non measurable set $D\subset \Bbb{R}$ intersect every closed uncountable sets.
If the conjecture can be proved to be true then it will help me to solve this question easily.
UPDATE:
The conjecture is false.
Let $D\subset \Bbb{R}$ be saturated non measurable set and $F$ be a closed uncountable set of measure $0$.
Then $A=D\setminus F$ is a saturated non measurable set as $A\subset D$ and $A^c\subset F$ and $m_i(D) =0=m_i(F) =m(F) $.
But clearly $A$ doesn't intersect $F$.
Dense set may not intersect every closed uncountable sets.
Saturated non measurable set may not intersect every closed uncountable sets.
Question:Under what conditions does a non measurable dense set necessarily intersect every closed uncountable set?