\message{ !name(/home/lukstafi/pmwiki-mode/preamble_tikz.tex)}\documentclass{article}

\usepackage{preview}

\usepackage[a3paper,dvips]{geometry}

\usepackage{amssymb,amsmath}
\usepackage{enumerate}
\usepackage{url}
\usepackage{stmaryrd}
\usepackage{subfigure}
\usepackage[dvips]{graphicx}

\usepackage[all,dvips]{xy}
\usepackage{pgf}
\usepackage{tikz}
\usetikzlibrary{shapes}
\usetikzlibrary{arrows}
%\usepackage{msc}
%\usepackage{gastex}

\pagestyle{empty}

\begin{document}

\message{ !name(<none>) !offset(-10) }
\begin{center}
\begin{tikzpicture}[thick,scale=2]
    
    \draw (-0.8,-0.5) node {$\mathcal{G} := $};
    \draw (0,0) node[above=2pt,color=red!80!black] {\small $v_0$};
    \draw (0,0) node(a) {$\bullet$};
    \draw (1,0) node(b) {$\bullet$};
    \draw (0,-1) node(c) {$\bullet$};
    \draw (1,-1) node(d) {$\bullet$};
    \draw[->] (a) -- (b);
    \draw[->] (a) -- (c);
    \draw[->] (c) -- (d);

\end{tikzpicture}
\end{center}
\message{ !name(/home/lukstafi/pmwiki-mode/preamble_tikz.tex) !offset(-18) }

\end{document}