\documentclass{article}
\usepackage{mathptmx}
\usepackage{tikz}
\usepackage[utf8]{inputenc}
%\usepackage{color}
\usepackage[active,pdftex,tightpage]{preview}
\PreviewEnvironment[]{tikzpicture}
\PreviewEnvironment[]{pgfpicture}
\DeclareSymbolFont{symbolsb}{OMS}{cmsy}{m}{n}
\SetSymbolFont{symbolsb}{bold}{OMS}{cmsy}{b}{n}
\DeclareSymbolFontAlphabet{\mathcal}{symbolsb}

\usetikzlibrary{positioning}

\tikzset{
  >=stealth
}

\begin{document}
<>
\end{document}
