File:Krausz-Partition 3.png

\documentclass[convert=true, tikz]{standalone}

\begin{document}
\begin{tikzpicture}
  \node (s1) at (0,0) [shape=circle, draw] {$S_1$};
  \node (s2) at (2,0) [shape=circle, draw] {$S_2$};
  \node (s3) at (2,2) [shape=circle, draw] {$S_3$};
  \node (1) at (4,0) [shape=circle, draw] {$1$};
  \node (3) at (-2,0) [shape=circle, draw] {$3$};
  \node (6) at (-2,2) [shape=circle, draw] {$6$};

  \draw (3) -- (s1) -- (6);
  \draw (1) -- (s2) -- (s1) -- (s3) -- (s2);
\end{tikzpicture}
\end{document}