Let $A, B$ and $D$ be non-empty subsets of $\mathbb{C}$.
Assume that
$A\cap \partial B\neq\varnothing$
$B\subset D$.
$\overline{B}=\overline{D}$.
Is $A\cap \partial D\neq\varnothing$?
Let $A, B$ and $D$ be non-empty subsets of $\mathbb{C}$.
Assume that
$A\cap \partial B\neq\varnothing$
$B\subset D$.
$\overline{B}=\overline{D}$.
Is $A\cap \partial D\neq\varnothing$?
NO. Take $B=\mathbb Q, A=D=\mathbb R$ for a counter-example.