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. $2/{\it\tau}$.