,t), \quad (x,t) \in {\mathcal {U}}_{\delta ,T}. \end{aligned}$$\end{document}$$In view of ([0](#Equ0){ref-type=""}) the function $\documentclass[00pt]{minimal}                 \usepackage{amsmath}                 \usepackage{wasysym}                  \usepackage{amsfonts}                  \usepackage{amssymb}                  \usepackage{amsbsy}                 \usepackage{mathrsfs}                 \usepackage{upgreek}                 \setlength{\oddsidemargin}{-00pt}                 \begin{document}$${\varvec{v}}(x,t)