A countable set derived by fuzzy set

In this paper, it shows that for each fuzzy set $u$ on ${\mathbb{R}}^m$, the set $D(u)$ is at most countable. Based on this, it modifies the proof of assertion (I) in step 2 of the sufficiency part of Theorem 4.1 in paper: Characterizations of compact sets in fuzzy sets spaces with $L_p$ metric, http://arxiv.org/abs/1509.00447.