[boost] [graph]matching example is not consistent

Hello, I found some inconcistency on the following example: http://www.boost.org/doc/libs/1_53_0/libs/graph/example/matching_example.cpp This code has graph diagrams as follows: 0 1---2 3 \ / \ / 4---5 6---7 | | | | 8---9 10---11 / \ / \ 12 13 14---15 16 17 Vertices 1 and 2 is connected on the diagram. But "add_edge(1,2,g)" isn't called. I attached the patch that adds the code above. After applying the patch, result is changed. But I think that the essence of the example is not changed. Thanks, Taka