[graph-tool] add_edge_list() and undirected graph

Given an *undirected* graph g with four vertices, I add edges by g.add_edge_list([(0, 1), (0, 2), (0, 3), (1, 0), (1, 2), (1, 3), (2, 0), (2, 1), (2, 3), (3, 0), (3, 1), (3, 2)]) . When calling g.num_edges() the result is 12. In my opinion it should be 6, as the graph is undirected? Any ideas? -- Christopher Morris Algorithm Engineering, Department of Computer Science, TU Dortmund University https://ls11-www.cs.tu-dortmund.de/staff/morris