引用:

\usepackage{amsmath}
\usepackage{amssymb}
\usepackage[usenames]{color}
%\definecolor{myColor}{RGB}{0,128,255}
%\pagecolor{white}\color{myColor}


%make in-line math becaome displaystyle math for all the time
\everymath{\displaystyle}

%define vector, use it as \Rvector{AB}
\makeatletter
\def\rightharpoonupfill@{\arrowfill@\relbar\relbar\rightharpoonup}
\newcommand{\Rvector}{%
  \mathpalette{\overarrow@\rightharpoonupfill@}}
\makeatother

% define "such that"
\newcommand{\suchthat}{\mathrel{\ooalign{$\ni$\cr\kern-1pt$-$\kern-4.5pt$-$}}}