The extension problem of the mean curvature flow (I)

We show that the mean curvature blows up at the first finite singular time for a closed smooth embedded mean curvature flow in R3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\mathbb {R}}}^3$$\end{document}.