绘制 tikz 自动机时缺少 \endcsname 插入

Question

我正在使用提供的示例这里，代码为：

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{automata}
\usetikzlibrary{positioning} 
\usetikzlibrary{arrows}       
\tikzset{node distance=2.5cm, 
         every state/.style={
          semithick,fill=gray!10},
          initial text={}, 
          double distance=2pt, 
          every edge/.style={
          draw, ->,>=stealth’, 
          auto,semithick}}
\let\epsilon\varepsilon


\begin{document}
\begin{tikzpicture}
\node[state, initial] (q1) {$q_1$};
\node[state, accepting, right of=q1] (q2) {$q_2$};
\node[state, right of=q2] (q3) {$q_3$};
\end{tikzpicture}
\end{document}

但我一直收到“缺少 \endcsname 插入”错误，请帮忙。