% TeX root = ../main.tex
\begin{tikzpicture}
\node[state,initial] (l0) ;
\node[state] (l1) [below=1.2cm of l0] ;
\node[state] (l2) [below right=of l1] ;
\node[state] (l2') [below left=of l1] ;
\node[state] (l3) [below right=of l2] ;
\node[state] (l3') [below left=of l2,gray] ;
\node[] (l4) [below right=of l3] ;
\node[] (l4') [below left=of l3] ;
\path[->] (l0) edge node (l1)
(l1) edge node[swap] (l2')
edge node (l2)
(l2) edge[gray]node[gray,swap] (l3')
edge node[] (l3)
;
\path[dotted,->]
(l3) edge[gray] (l4')
edge (l4)
;
\end{tikzpicture}