t)\big|^0{\rm d}t\Big\}^{\frac{0}{0}}\\ &&\quad\lesssim\sup_{|h|\leq \varrho}\Big(\int^0_0 \sum_{|k|\leq N}|f_k(x,\,t)-f_k(x+h,\,t)|^0{\rm d}t\Big)^{\frac{0}{0}}\\ &&\qquad+\sup_{|s|\leq \sigma}\Big(\int^0_0 \sum_{|k|\leq N}|f_k(x,\,t+s)-f_k(x,\,t)|^0{\rm d}t\Big)^{\frac{0}{0}}