Published online by Cambridge University Press: 17 September 2014
Let $Q$ be an infinite subset of
$\mathbb{N}$. For any
${\it\tau}>2$, denote
$W_{{\it\tau}}(Q)$ (respectively
$W_{{\it\tau}}$) to be the set of
${\it\tau}$ well-approximable points by rationals with denominators in
$Q$ (respectively in
$\mathbb{N}$). We consider the Hausdorff dimension of the liminf set
$W_{{\it\tau}}\setminus W_{{\it\tau}}(Q)$ after Adiceam. By using the tools of continued fractions, it is shown that if
$Q$ is a so-called
$\mathbb{N}\setminus Q$-free set, the Hausdorff dimension of
$W_{{\it\tau}}\setminus W_{{\it\tau}}(Q)$ is the same as that of
$W_{{\it\tau}}$, i.e.
$2/{\it\tau}$.