Arithmetic on Moran sets

Let $(\mathcal{M},c_k,n_k)$ be a class of Moran sets. We assume that the convex hull of any $E\in (\mathcal{M},c_k,n_k)$ is $[0,1]$. Let $A,B$ be two non-empty sets in $\mathbb{R}$. Suppose that $f$ is a continuous function defined on an open set $U\subset {\mathbb{R}}^2$. Denote the continuous image of $f$ by \begin{equation*} f_{U}(A,B)={f(x,y):(x,y)\in (A\times B)\cap U}. \end{equation*} In this paper, we prove the following result. Let $E_1,E_2\in (\mathcal{M},c_k,n_k)$. If there exists some $(x_0,y_0)\in (E_1\times E_2)\cap U$suchthat$$\sup_{k\geq 1}\left{1-c_kn_k\right}<\left\vert \frac{\partial {y}f|{(x_{0},y_{0})}}{\partial {x}f|{(x_{0},y_{0})}}\right\vert <\inf_{k\geq 1}\left{\dfrac{c_k}{1-n_kc_k}\right},$$then$f_U(E_1, E_2)$ contains an interior.