Special Graphs

3. A multigraph is a graph that may contain parallel edges or loops.
   

   This graph is a multigraph because it contains multiple edges between the same pair of vertices. Miriam Briskman, CC BY-NC 4.0.

   \documentclass[border=1pt]{standalone}
   \usepackage{tikz}
   
   \tikzset{
   vertex/.style={draw, circle, very thick, minimum size=1cm},
   edge/.style={very thick}
   }
   
   \begin{document}
   
   \begin{tikzpicture}
   
   \node[vertex] (v1) at (0,0) {$1$};
   \node[vertex] (v2) at (3,0) {$2$};
   
   \draw[edge] (v1) to[bend left=25] (v2);
   \draw[edge] (v1) to[bend right=25] (v2);
   
   \end{tikzpicture}
   
   \end{document}